SCIENCE

Chapter 1 Chemical Reaction and Equation

Important Questions 

1. What happens chemically when quick lime is added to water ?

Ans. Quick lime reacts vigorously with water to produce calcium hydroxide releasing a large amount of heat.

CaO(s) + H2O – Ca(OH)2

2. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green . Predict the new compound formed which imparts a blue-green colour to the solution.

Ans. The new compound formed is cuprous chloride. It imparts a blue-green colour to the solution.

CuO(s) + 2HCL(aq) – CuCl2(aq) + H2O

3. Why is respiration considered an exothermic process ?

Ans. We need energy to stay alive. We get this energy from the food we eat. During disgestion, the food is broken down to simple substances, For example rice, potatoes etc,. contain starch which is broken down to glucose. During respiration, glucose is oxidised to CO2 and H2O with the help of oxygen inhaled during respiration. Energy is evolved in this process.

C6H12O6(aq) + 6O2(g) – 6CO2(g) +H2O(l) + Heat

4. Potato chips manufacturers fill the packet of chips with nitrogen gas. Why ?

Ans.  Flushing bags of chips with nitrogen cuts off oxygen and protects the food from rancidity.

5. If copper metal is heated over a flame it develops a coating. What is the colour and composition of coating ?

Ans. We get a black coating of CuO, copper oxide.

6. Write a balanced chemical equation to represent the following reaction :

Carbon monoxide reacts with hydrogen gas at 340 atm to form methyl alcohol

Ans. CO(g) + 2H2 – (340 atm) CH3OH(l)

7. Which one is a chemical change – fermentation of fruit juice or diluting fruit juice ?

Ans. Fermentation of fruit juice is a chemical change.

8. Is burning of a candle wax a physical change or a chemical change ?

Ans. It is a chemical change. Thy hydrocarbon of wax burns to produce CO2 and H2O.

9. State one basic difference between a physical and chemical change.

Ans. No new substance is formed in a physical change while a new substance is formed in a chemical change.

10. Name ans state the law which is kept in mind when we balance a chemical equation.

Ans. While balancing a chemical equation, we follow the law of conservation of mass which states : matter can neither be created nor destroyed in a chemical reaction.

11. What is an oxidation reaction ? Identify in the following reaction :

(i) The substance oxidised and the substance reduced

ZnO + C – Zn + CO

Ans. Oxidation reaction is one which involevs gain of oxygen or loss of hydrogen.

(i) C is oxidised to CO and ZnO is reduced to Zn.

12. When potassium iodide solution is added to a solution os lead(ii) nitrate in a test tube, a precipitate is formed.

(i) What is the colour of this precipitate ?

(ii) Name the compound precipitated.

(iii) Write the balanced chemical equation for this reaction.

(iv) What type of reaction is this?

Ans. (i) The colour of the precipitation is yellow.

(ii) The compound precipitated is lead iodide(PbI2)

(iii) The balanced chemical equation for this reaction is :

Pb(NO3)2)(aq) + 2KI(aq) – PbI2(s) + 2KNO3()aq

(iv) It is a double displacement reaction.

13. What is a redox reaction ? Write down a chemical equation representing it.

Ans. A reaction in which one reactant gets oxidised while the other gets reduced is called redox reaction.

ZnO + C – Zn + CO

Zinc oxide is reduced to zinc while carbon is oxidised to carbon monoxide.

14. When a green compound is heated strongly, its colour changes to black and odour of burning sulphur is given out.

(a) Name the compound

(b) State the type of reaction.

(c) Write the chemical equation involved.

Ans. (a) The green compound is FeSO4.

(b) It is thermal decomposition reaction.

(c) 2FeSO4 (s) -(Heat) Fe2O3 (s) + SO2(g) + SO3 (g)

15. A white compound on heating decomposes to give brown fumes and a yellow residue is left behind. Name the compound. Write the chemical equation of the reaction stating its type.

Ans. The compound is lead nitrate, Pb(NO3)2

The reaction involved is

2Pb(NO3)2 – (Heat) 2 Pb(NO3)2

16. A light sensitive compound ‘X’ of silver is used in black and white photography. On exposure to sunlight its colour changes to grey.

(a) Identify ‘X’.

(b) Write a chemical equation to express the above change.

(c) Identify the type of chemical reaction.

Ans. (a) The compound X is silver bromide. AgBr.

(b) The chemical equation for the change is

2AgBr – (sunlight) 2Ag + Br2

(c) It is a photochemical decomposition reaction.

17. Solutions of lead nitrate and potassium iodide are mixed in a test tube.

(a) Write the chemical equation involved in a balanced form.

(b) What is the colour of the precipitate ? Name the precipitate.

Ans. (a) The chemical equation involved is

Pb(NO3)2 + KI – PbI2 + KNO3

(b) Colour of the precipitate is yellow. It is lead iodide, PbI2

18. Why do we store silver chloride in dark coloured bottles ? Explain in brief.

OR

A small quantity of silver chloride is kept in the sunlight in a china dish for about half an hour.

(i) State the change you would observe in the colour of silver chloride. Suggest a reason for this change.

(ii) Write balanced chemical equation for the reaction taking place in this case. 

Ans. Silver chloride on exposure to sunlight decomposes according to the following equation :

2AgCl – (sunlight) Ag + Cl2

That is why silver chloride is kept in dark coloured bottles.

19. Why do silver articles turn black and copper items turn green after sometime ?

Ans. Silver articles turn black and copper items turn green after sometime.

This is because these metals are attacked by moisture, acids etc. present in the atmosphere.

The black colour on silver is due to the formation of Ag2S and green colour on copper items is due to the formation of CuCO3.

20. Why do fire flies glow at night ?

Ans. Fire flies have a protein which in the presence of an enzyme undergoes aerial oxidation. This is a chemical reaction which involves emission of visible light. Therefore, fire flies flow at night.

21. Name the substances oxidised and redused, and also identify the oxidising agents and reducing agents in the following reactions :

(i) Fe2O3 + 3CO – 2Fe + 3CO2

(II) 3MnO2 + 4Al – 3Mn + 2Al2O3

(iii) H2S + SO2 – S + H2O

Ans.  Fe2O3 + 3CO – 2Fe + 3CO2

Fe2O3 is reduced because oxygen has been reduced and CO is oxidised because O has been added to it. Fe2O3 has acted as oxidising agent and CO has acted as reducing agent.

(ii) 3MnO2 + 4Al – 3Mn + 2Al2O3

MnO2 is reduced because O has been removed from it to give Mn. Al has been oxidised because O has been added to it to obtain Al203. MnO2 is the oxidising agent while Al is reducing agent.

(iii) 2H2S + SO2 – 3S + 2H2O

H2S has lost H to change into S. Thus, it has been oxidised. SO2 has lost O to change into S. Thus, it has been reduced. H2S acted as reducing agent while SO2 has acted as oxidising agent.

21. (a) A solution of a substance ‘X’ is used for testing carbon dioxide. What will be the reaction of ‘X’ with carbon dioxide ? Write balanced equation for this reaction .

(b) How is ‘X’ obtained ? Give chemical equation.

Ans. ‘X’ is calcium hydroxide or slaked lime.

‘X’ reacts with carbon dioxide to form calcium carbonate which appears as a white precipitate. The balanced equation for this reaction is :

Ca(OH)2 + CO2 – CaCO3 + H2O

(b) ‘X’ i.e., calcium hydroxide is obtained by adding water to quick lime(CaO) as per the following equation :

CaO + H2O – Ca(OH)2

22. (a) Can we stir silver nitrate solution with a copper spoon ? Why of why not ? Support your answer with reason.

(b)  Why a brown coating is formed on the iron rod when iron rod is kept dipped in copper sulphate solution for sometime ? What change will be observed in the colour of the solution ?

(c) A green coating develops on the copper vessel in the rainy season. Why ?

Ans. (a) We cannot stir silver nitrate with a copper spoon. Copper being more reactive than than silver, displaces silver from silver nitrate, that is, a reaction will take place.

(b) Iron being more reactive than copper, displaces copper from copper sulphate by the following reaction :

Fe + CuSO4 – FeSO4 +Cu

Brown coating of copper is deposited on the iron rod. Colour of the solution becomes green due to the formation of ferrous sulphate.

(c) Copper reacts with moist carbon dioxide in the air in rainy season and a green coating is formed. this is due to the formation of copper carbonate.

23. (a) Illustrate an activity along with a labelled diagram, to show that a change in the state of matter and change in temperature takes place during a chemical reaction.

(b) Write balanced chemical equations for the following equations :

(i) Natural gas burns and combines with oxygen to produce carbon dioxide and water.

(ii) Ferrous sulphate crystals on heating break up into ferric oxide, sulphur dioxide and sulphur trioxide.

Ans. (a) Take about 5g of quick lime in a beaker and add to it about 50 ml of water. A brisk reaction takes place and a lot of heat is evolved.

CaO + H2O –  Ca(OH)2 + Heat

Quick lime is a white solid but after the reaction, calcium hydroxide is formed which is soluble in water and a clear solution is obtained. Thus, there has been a change in the state of matter and change in temperature.

(b) (i) CH4 + 2O2 +2H2O

(ii) 2FeSO4.7H2O -(Heat) Fe2O3 + SO2 + SO3 + 14H2O

Chapter 2 Acid Bases and Salt

Important Questions

1.How will you test a gas which is liberated when hydrochloric acid reacts with an active metal ?

Ans. The gas produced when hydrochloric acid reacts with an active metal is hydrogen gas. The gas is passed through soap solution when soap bubbles are formed. Hydrogen gas being lighter than air. these bubbles rise up. When a burning candle is brought near soap bubbles containing hydrogen gas, a pop sound is heard due to the combustion of hydrogen to form water.

2H2 + O2 – 2H2O

2. Why does the flow of acid rain water into a river make the survival of aquatic life in the river difficult ?

Ans. When acid rain water flows into the river, it makes the river water acidic. Animals need a pH of 7 – 7.8 for survival. When acid rain water flows into the river, the pH of river water becomes less than 7. This makes the survival of aquatic life in the river difficult.

3. At what pH in the mouth is tooth decay faster and why ?

Ans. At pH lower than 5.5 in the mouth, tooth decay becomes faster because the acid produced reacts with the enamel of the teeth and corrodes it.

4. Write balanced chemical equations for the reactions taking place when dry blue crystals of copper sulphate are dropped into concentrated sulphuric acid.

Ans. Concentrated sulphuric acid is a powerful dehydrating agent. It takes out water of crystallisation from the crystals of copper sulphate leaving behind anhydrous white powder of CuSO4.

CuSO4.5H2O – CuSO4 + 5H2O

5. A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify the compound and write its chemical formula.

Ans. The compound is Plaster of paris, CaSO4. 1/2 H2O

6. Name the acid present in (i) nettle sting (ii) curd.

Ans. The acid present are as under :

(i) Nettle sting : Methanoic acid   (ii) Curd : Lactic acid

7. Name a salt which does not contain water of crystallisation.

Ans. Sodium hydrogencarbonate (NaHCO3) does not contain water of crystallisation.

8. What happens when nitric acid is added to egg shell ?

Ans. Egg shell contains calcium carbonate. The following reaction will take place :

CaCO3 + 2HNO3 – Ca(NO3)2 + CO2 + H2O

9. How will you distinguish between baking powder and washing soda by heating ?

Ans. ON heating baking powder, CO2 gas is liberated when turns lime water milky.

2NaHCO3 – Na2CO3 + H2O + CO2

No gas is liberated on heating washing soda.

Na2CO3.10H2O – Na2CO3 + 10H2O

10. What is baking powder ? How does it make the cake soft and spongy ?

Ans. Baking powder is a mixture of sodium hydrogencarbonate and a mild edible acid like tartaric acid. When baking powder is heated or mixed with water, the following reaction takes place :

NaHCO3 + H+ – CO2 + H2O + Sodium salt of acid

11. What is the chemical formula for Plaster of Paris ? How is it prepared ? State the common and chemical names of the compound formed when Plaster of Paris is mixed with water.

Ans. The chemical formula for Plaster of Paris is CaSO4.1/2H2O. It is prepared by heating gypsum at 373 K as shown by the chemical equation :

CaSO4.2H2O – CaSO4.1/2H2O +3/2H2O

WHen Plaster of Paris is mixed with water, gypsum (common name) is formed again. Chemically it is known as calcium sulphate dihydrate.

CaSO4.1/2H2O + 3/2H2O – CaSO4.2H2O

12. How is bleaching powder prepared ? why does bleaching powder

(i) smell strongly of chlorine ?

(ii) not dissolve completely in water ?

Ans. Bleaching powder is prepared by the action of Cl2 on dry slaked lime.

Ca(OH)2 + Cl2 – CaOCl2 + H2O

Bleaching powder smells strongly of chlorine because it is loosely bound to slaked lime. Carbon dioxide present in the air combines with bleaching powder liberating chlorine.

CaOCl2 + CO2 – CaCO3 + Cl2

Bleaching powder reacts with water as under :

CaOCl2 + H2O – Ca(OH)2 + Cl2

Ca(OH)2 + CO2 – CaCO3 + H2O

Calcium carbonate is an insoluble substance. Hence, bleaching powder does not dissolve in water completely.

13. A knife, which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution. If the colour of the solution is changed is red, what inference can be drown about the nature of the fruit and why ?

Ans. The fruit is a citrus fruits because fruits contain an acid. The acid sticking to the knife turns blue litmus into red.

14. You might have seen lemon or tamarind juice being used to clean tarnished surface of copper vessels. Explain why these sour substances are effective in cleaning the vessels.

Ans. Lemon juice contains citric acid while tamarind contains tartaric acid. These acids act as cleansing agents. They react with the layer of copper carbonate on the surface of vessels to form soluble salts which are washed away by water.

15. Why should curd and other sour foodstuffs not to be kept in brass of copper vessels ?

Ans. Curd and other sour foodstuffs contain acids which react with copper metal to form poisonous salts, which may cause food poisoning. Hence it is not advisable to keep curd and sour foodstuffs in brass or copper vessels.

16. How will you prove that the given salt is a carbonate of metal ?

Ans. Take about 1 g of the salt in a test tube. Add about 1 mL of dilute H2SO4. Pass vapours produced through lime water taken in another test tube. If the lime water turns milky, the salt is a carbonate of a metal.

17.  What are antacids ? Name two compounds which are used as antacids.

Ans. Antacids are mild bases which are used to neutralise the effect of excess acid produced in the stomach as a result of indigestion.

18. Dry HCl gas does not change the colour of dry blue litmus paper. Give reason.

Ans. Dry HCl gas does not contain H+ ions. These ions are produced when HCl gas comes into contact with water.

HCl + H2O – H3O+ + OH-

The H3O+ ions or H+(aq) react with blue litmus and the colour is changed to red.

19. Though the compounds such as glucose and alcohol have hydrogen atoms in their molecule, yet they are not categorised as acids. Why ?

Ans. Substances which furnish H+ ions on dissolving in water act as acids. Glucose and alcohol do not furnish H+ ions in water. Hence they are not categorised as acids.

20. Classify the following salts into acidic, basic or neutral :

Potassium sulphate, ammonium chloride, sodium carbonate, sodium chloride.

Ans. Acidic salts : Ammonium chloride

Basic salts : Sodium carbonate

Neutral salts : Potassium sulphate, sodium chloride

21. In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by- product. The gas X reacts with dry slaked lime to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y.

Ans. During the manufacture of sodium hydroxide by electrolysis of sodium chloride, chlorine gas is formed as a by-product. It reacts with dry slaked lime, Ca(OH)2 to form bleaching powder CaOCl2, which is used as a bleaching agent in chemical industry.

22. A dry pellet of a common base B, when kept in open, absorbs moisture and turns sticky. The compound is also a by-product of CHlor-alkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide ?

Ans. Sodium hydroxide is produced as a by-product in chlor-alkali process, along with Cl2 and H2. Pallet of NaOH when kept in open absorbs moisture and turns sticky.

2NaOH + CO2 – Na2CO3 + H2O

23. Explain the effect on concentration of hydronium ion [H3O]+ and pH of an acidic solution on dilution.

Ans. Concentration of hydronium ion [H3O]+ decreases on dilution of an acidic solution because the same number of [H3O]+ ions are present in a larger volume.

pH of the acidic solution increases on dilution because the concentration of H+ ions decreases. Lower the H+ ion concentration higher the pH value.

24. What is meant by water of crystallisation ? How would you show that copper sulphate crystals contain water of crystallisation ?

Ans. Water which is present in the crystals of a compounds is called water of crystallisation . It is defined as the fixed number of water molecules present in one formula unit of a salt.

Copper sulphate crystals are blue in colour. On heating solid copper sulphate crystals, they lose water of crystallization and become white. On adding a few drops of water to the white powder, blue colour of copper sulphate is restored. This shows that copper sulphate crystals contain water of crystallisation.

25. While constructing a house, a builder selects marble flooring and marble table top for the kitchen where vinegar and juices of lemon tamarind etc, are more often used for cooking. Will you agree to this selection and why ?

Ans. No, this selection is wrong.

Vinegar and tamarind etc contains acid. Acid react with marble flooring and marble table top. Marble is calcium carbonate which reacts with acids.

Chapter 3 Metals and Non Metals

Important Questions

1. An element A forms two oxides AO and AO2. The oxide AO is neutral wheras the oxide AO2 is acidic in nature. would you call element A a metal or a non-metal ?

Ans. Element A is a non-metal. Only non-metals form neutral and acidic oxides.

2.  A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.

Ans. X = Carbon, Y = Diamond, Z = Graphite

3. Give an example of a metal which is a liquid at room temperature.

Ans. Mercury(Hg).

4. Why do silver ornaments lose their shine when kept for sometime ?

Ans. They get tarnished by reacting with atmospheric gases to produce silver sulphide.

5.  Name the metal which has very low melting point and can melt with the heat of you palm.

Ans. Gallium/Caesium.

6. Choose the amphoteric oxides amongst the following :

Na2O, ZnO, Al2O3, CO2, H2O

Ans. ZnO and Al2O3

7. Name one metal which react with very dilute HNO3 to evolve hydrogen gas.

Ans. Magnesium and manganese react with very dilute HNO3 to evolve hydrogen gas.

8. How do we know whether a given element is a non-metal if we know its electronic configuration ?

Ans. If there are four or more than four electrons in the valence cell of the given element, it is a non-metal.

9. What kind of compounds are called ionic compound ?

Ans. Compounds formed by the transfer of electrons from one atom to the other, are called ionic compounds.

10. Define metallurgy.

Ans. The process of extraction of a metal form its ore is called metallurgy.

11. Differentiate between roasting and calcination processes giving one example of each.

Ans. Roasting : Sulphide ore is strongly heated in the presence of air into metal oxide.   2ZnS + 3O2 – 2ZnO + 2SO2

Calcination : Carbonate ore is strongly heated in the absence of air into metal oxide.  ZnCO3 – ZnO + CO2

12. A substance X which is an oxide of a metal is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Ans. The substance X is calcium oxide, CaO.

The element calcium is present in bones On treatment with water, it produces calcium hydroxide as under :

CaO + H2O – Ca(OH)2

Calcium hydroxide is a base. It turns red litmus blue.

13. A metal A which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.

Ans. The metal A is aluminium Al.

The substance B is Al2O3 which is amphoteric because it reacts with both acid and base.

Al2O3 + 6HCl – 2Al2O3 + 3H2O

Al2O3 + 2NaOH – 2NaAlO2 + H2O

14. Why is sodium kept immersed in kerosene oil ?

Ans. Sodium reacts with ari so vigorously that it catches fire if kept in the open. Hence to protect it and prevent accidental fires, it is kept immersed in kerosene oil. Sodium also reacts with water to evolve hydrogen gas.

15. What are amphoteric oxides ? Give two examples of amphoteric oxide with balanced chemical equation.

Ans. An oxide which reacts with acids as well as bases to produce salt and water is called amphoteric oxide.

Al2O3 + 6HCl – 2AlCl3 +3H2O

Al2O3 + 2NaOH – 2NaAlO2 + H2O

16. Zinc does not evolve hydrogen gas on reacting with HNO3.

Ans. Nitric acid is a strong oxidising agent. It oxidises hydrogen produced to form water and is itself reduced to oxide of nitrogen.

17. Explain why calcium metal after reacting with water starts floating on its surface. Write the chemical equation for the reaction.

Ans. Calcium reacts with water to form hydrogen gas. The bubbles of hydrogen formed stick to the surface of calcium. Hydrogen gas being lighter, calcium starts floating on water.

Ca + 2H2O – Ca(OH)2 + H2

18. Write four important purposes of making alloys.

Ans. To increase hardness, To increase resistance towards corrosion, To modify reactivity, to lower melting point

19. Why do silver articles turn black and copper items turn green after sometime ?

Ans Silver articles turn black after sometime due to the formation of silver sulphide. Ag2S layer on it.

Copper items turn green after sometime due to the formation of copper carbonate layer on it.

20. Metals are said to be shiny. Why do metals generally appear to be dull ? How can their brightness be restored ?

Ans. Metals like copper and silver appear to be dull because of corrosion due to sulphur, carbon dioxide and moisture present in the atmoshphere.

Brightness of the metals can be restored by rubbing with a cloth moistened with a dilute acid.

21. Explain how, mercury is extracted from its sulphide ore cinnabar. Give chemical equations of the reactions involved.

Ans. When cinnabar is heated in air, It is first converted into mercury oxide (HgO). Mercury oxide on further heating is reduced to mercury.

HgS + 3O2 -(Heat) 2HgO + 2SO2

2HgO -(Heat) 2Hg + O2

22. Explain The following terms :

(i) Mineral (ii) Ore (iii) Gangue.

Ans. (i) Mineral : Elements or compounds which occur in their natural form in the earth’s crust are called minerals.

(ii) Ores : Minerals from which a metal can be extracted profitably are called ores.

(iii) Gangue : Impurities such as soil and sand which are present in the minerals or ores are called gangue.

23. What is concentration of an ore ? Why is it necessary to concentrate an ore before processing ? Name an ore of mercury and copper .

Ans. The process of removing unwanted impurities like sand, soil, etc. , present in an ore is called concentration of the ore.

We need to concentrate the ore so that the impurities do not interfere in the extraction of the metal.

Ore of mercury : cinnabar (HgS)

Ore of copper : copper pyrite(Cu2S)

24. Give reasons :

(i) Silver metal does not easily combine with oxygen but silver jewellary tarnishes after sometime.

(ii) Iron grills are frequently painted.

(iii) Gold ornaments retain their luster even after several years of use.

Ans. (i) Silver metal reacts with the H2S gas present in traces in the atmosphere to form silver sulphide which tarnishes the metal.

(ii) Iron forms a layer of rust (Fe2O3.xH2O) on combination with oxygen and moisture present in the atmosphere. This weakens the metal. To prevent this loss iron grills are frequently painted.

(iii) Gold is an unreactive metal. It does not react with atmospheric oxygen and acids. So the lustre of gold jewellery is retained even after several years.

25. A gas is produced when conc. H2SO4 is added to solid sodium chloride taken in a test tube. The gas coming out of the delivery tube is passed over a dry blue litmus paper and then over a moist blue litmus paper. what would you observe ? Explain reason with the help of a chemical equation.

Ans. HCl gas is produced when conc.H2SO4 is added to solid sodium chloride.

NaCl + H2SO4 -NaHSO4 + HCl

HCl gas when passed over dry blue litmus paper shows no effect.

HCl gas when passed over moist blue litmus paper turns it red.

This is because dry HCl gas does not produce H+ ions, therefore there is no action on dry blue litmus paper.

Moist blue litmus paper contains water. HCl gas when passed over moist blue litmus paper reacts with water to form H+ ions. An acid turns blue litmus red. Therefore, a red colour will be obtained.

26. Give reasons for the following :

(i) Carbonate and sulphide ores are usually converted into oxides during the process of extraction of metals.

(ii) Ionic compounds have generally high melting points.

(iii) Hydrogen is not a metal, but it has been assigned a place in the reactivity series of metals.

(iv) The galvanised iron article is protected against rusting even if the zinc layer is broken.

(v) The wires carrying current in homes have a coating of PVC.

Ans. (i) It is easier to convert metal oxides to metals as compared to carbonates and sulphides. Therefore carbonates are calcinated and sulphides are roasted to oxides.

(ii) There are electrostatic forces of attraction between the cations and anions in ionic compounds which are difficult to break. Therefore ionic compounds have high melting points.

(iii) Metals above hydrogen evolve hydrogen gas and metals below hydrogen do not evolve hydrogen when treated with an acid. That is when hydrogen has been assigned a place in the reactivity series of metals.

(iv) Even if zinc layer is broken, it will preferentially oxidised because it is more reactive than iron.

(v) The wires carrying current in homes have a coating of PVC. This is because PVC is an insulating substance and protects from electric shock.

Chapter 6 Life Processes

Important Questions

1.  Name the components of blood which transport :

(i) Food, carbon dioxide and nitrogenous wastes,

(ii) Oxygen.

Ans. Blood pasama, (ii) RBC.

2. Rings of cartilage are present in trachea. Why ?

Ans. From nostril, the air passes through pharynx into lungs via trachea. Incomplete C – shaped rings of cartilage are present in the trachea which ensure that the air –  passage does not collapse when there is no air in it.

3. What will happen to plant if its xylem is removed ?

Ans. Movement of water and mineral from soil to other parts of plant will stop and the plant will ultimately die if its xylem is removed.

4. Name the green dot like structures in some cells observed by a student when a leaf peel was viewed under a microscope. What is this green colour due to ?

Ans. The green dots indicate chloroplast and the green colour is due to chlorophyll pigment present in chloroplast.

5. Give one reason why multicellular organisms require special organs for exchange of gases between their body and their environment.

Ans. In multi-cellular organisms all the cells are not in direct contact with the surrounding environment. Thus simple diffusion does not meet the requirement of all the cells.

6. (i) Name the respiratory pigment found in human beings.

(ii) How is carbon dioxide transported in our body ?

Ans. (i) Haemoglobin

(ii) Generally diffused in blood plasma, as carbonate ions and as carbiaminohaemoglobin.

7. (a) Why are cramps caused in our muscles during sudden activity ?

(b) Name the type of respiration that takes place in yeast during fermentation.

Ans. (a) In our skeletal muscles pyruvate is converted into lactic acid and energy where there is deficiency of oxygen. Accumulation of lactic results in muscular cramps.

(b) Anaerobic respiration.

8. Name the following

(i) The three carbon molecule that is formed due to break-down of glucose during respiration.

(ii) The nitrogenous waste that is removed from the blood in our kidneys.

(b) How do unicellular organisms generally remove waste ?

Ans. (a) (i) Pyruvic Acid/ Pyruvate

(ii) Urea

(b) The undigested food material reaches the rear end of the organism and is thrown out by the process of exocytosis. The membrane of the vesicle fuses with the surface membrane.

9. (i) Name two organisms that obtain food through parasitic nutritive strategy.

(ii) How do fungi obtain their food ?

Ans. (i) Cuscuta, tapeworm obtain food through parasitic nutritive strategy.

(ii) Fungi are saprophytic and obtain food through dead and decaying matter.

10. Give Reasons :

(i) Fine hair and mucus are present in the nasal passage.

(ii) Rings of cartilage are present in the throat.

Ans. (i) Fine hair and mucus are present in the nasal passage so that any dust particles, pathogens etc., can be trapped in here and only clean air will enter the lungs. This is one of the defence mechanism of our body.

(ii) Rings of cartilage are present in the throat so that the trachea does not collapse on respiration.

11. Explain how are the fats digested in our bodies ? Where does this process take place ?

Ans. Fats are digested in small intestine. When food enters small intestine bile juice secreted by liver emulsifies fat and then the enzyme lipase which is secreted by pancreas coverts fat into fatty acid and glycerol.

12. Explain why the transportation of materials is necessary in animals.

Ans. The transport of substances like oxygen, Food, water, enzymes, hormones inside the body of organisms is called internal transport. Blood transports many substances like salts, vitamins, hormones, waste products. We thus need a pumping organ to push blood around the body. The transport system in human beings consist of heart, blood vessels(arteries, veins and capillaries) and circulatory fluid(blood and lymph).

Kidneys perform two main vital functions : (i) filtering the nitrogenous waste from the blood. (ii) osmoregulation i.e., maintaining the right amount of water and ionic balance in the body

All these substances are either required by various body cells or should be removed from body cells. Hence, transportation of material is necessary.

13. Describe the working of arificial kidney.

Ans. Artificial kidneys contain a number of tubes with a semi-permeable lining suspended in a tank filled with dialysing fulid. This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient’s blood is passed through these tubes. During this passage, the waste products from the blood pass into dialysing fluid by diffusion. The purified blood is then pumped back into the patient. This is similar to the function of the kidney, but it is different since there is no re-absorption involved.

14. Describe the prcess of digestion of food in man.

Ans. Process of digestion starts in mouth where secretion of three pairs of salivary glands known as saliva mixes with food. Saliva contains an enzyme ptyalin(Amylase) which digests starch and converts it into maltose.

From mouth food reaches the stomach where gastric glands are present having three types of cells. These cells secrete hydrochloric acid, protein digesting enzyme (pepsin) and mucus respectively. Small amount of gastric lipase is also present in the gastric juice secreted by these glands. Pepsin digests protein and converts it into peptones. Hydrochloric acid kills bacteria present in the food, prevents fermentation of semi-digested food and provides acidic medium which is essential for digestion of protein in stomach by the enzyme pepsin as it can act only in acidic medium. Gastric lipase partially breaks down lipids(fat) into glycerol and fatty acids.

From stomach semidigested food reaches the first part of small intestine called duodenum. It is a U shaped structure and receives the secretion of common duct. It brings secretions of liver(BIle) and pancreas (Pancreatic juice) to small intestine.

Bile emulsifies fat and converts fat molecules into small globules and changes the medium of food from acidic to alkaline.

Pancreatic juice contains following enzymes : (i) Trypsin (ii) Amylase (iii) Lipase

Trypsin digests protein and converts it into peptone and peptides.

Amylase digests fat and converts it into simple sugar.

Lipase digests fat and converts it into fatty acid and glycerol.

Wall of small intestine also have glands, a secretion of these glands is known as succus entericus. This intestinal juice completes the digestion of fat, protein and carbohydrate. In small intestine the final end product of protein is amino acid, of start is glucose, and fat is finally converted into fatty acid and glycerol in small intestine.

Finally, the digested food is absorbed by the wall of intestine which contains abundant finger like projections called villi which have rich supply of blood.

15. Describe double circulation in human beings. Why it is necessary ?

Ans. Double circulation is the passage of the same blood twice through the heart; first on the right side then on the left side in order to complete on cycle. Double circulation has two components :

Pulmonary circulation and systemic circulation.

Pulmonary circulation – It is the movement of blood form heart to the lungs and back. Deoxygenated blood of the body enters the right auricle, passes into right ventircle which pumps it into pulmonary arch. With the help of two separate pulmonary arteries the blood passes into the lungs. Here the arteries break up into arterioles and then capillaries for oxygenation. Capillaries join to form venules and then veins. Oxygenated blood comes back to the left auricle of heart through pulmonary veins.

Systemic circulation – It is the circulation of blood between heart and different parts of the body except lungs. Oxygenated blood received by left auricle passes into left ventricle. the left ventricle pumps it into aorta for supply to different body parts. Inside the organs the arteries break up into arterioles and then capillaries. Capillaries provide oxygen and nutrients to tissues. They receive carbon dioxide and wastes from the tissues. Capillaries unite to form venules which join to produce veins. Veins take the deoxygenated blood to the heart but now into the right auricle.

16. Briefly describe the process of transport of water and minerals in extremely tall plants ?

Ans. In higher plants water is absorbed through root hair, which are in contact with soil water. From root hair, the water moves through cortex and to the xylem elements. Once the water reaches root xylem, transpiration drives the water to move to the leaves through the stem. The upward movement of water from stem base to the tree top is called as “ascent of sap” Cohesion – adhesion theory proposed by Henry Dixon in 1914 is the most accepted theory of water movement in extremely tall plants.

According to this theory the steps involved can be summarized as follows :

(1) The evaporation of water from the stomata present in the leaves result in the movement of water from the neighboring cells i.e., the xylem vessels in the leaf. So evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots.

(2) The suction pressure works against the gravitational pull and is able to pull the water passively form the soil as a continuous water column due to cohesive-adhesive properties of water molecules from roots to the leaves.

(3). Cohesive force develops due to mutual attraction between water molecules. Adhesive force develops due to the attraction of water molecules to the lignocellulosic walls of xylem.

Thus transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to leaves in extremely tall plants.

Chapter 7 Control and Coordination

Important Questions

1.  Name the largest part of the hind-brain.

Ans. Cerebellum.

2. Name the system which facilitates the communication between the central nervous system and the other body parts of the body.

Ans. Peripheral nervous system.

3. State the role played by ovaries in a human female.

Ans. Ovaries produce mature ova which in turn produces a female sex hormone called estrogen. Estrogen is essential for development of secondary sex organs in female as well as secondary sexual characters like high pitch voice, development of mammary glands.

4. Name the longest cell present in the human body.

Ans. Neuron is the longest cell present in human body.

5. Name the gland and the hormone secreted by the gland, which are associated with following problems :

(i) a girl has grown extremely tall.

(ii) a woman has a swollen neck.

Ans. (i) Pituitary gland – Growth hormone.

(ii) Thyroid gland – Thyroxine hormone.

6. Trace the sequence of events through a reflex arc which occur when a bright light is focussed on your eyes.

Ans. Light – Eye – Sensory neuron – Central nervous system – Motor neuron – Effector muscle – Eye lids close.

7. “As the blood sugar level in our body falls insulin secretion is reduced.” Justify this statement in the reference of feedback mechanism that regulates the timing and amount of hormone released.

Ans. Insulin is a hormone that regulates our blood sugar level by converting it into glycogen which can be stored.

Hence, if there is more levels of sugar in blood then more insulin is produced and if the sugar level is less than insulin production is also reduced.

This is because of feedback mechanism where the blood sugar itself acts as a feedback for more or reduced insulin synthesis.

8. What is synapse ? In a neuron cell how is an electrical impulse created and what is the role of synapse in this context ?

Ans. Synapse is the gap/junction between two successive neurons.

All information from the environment is detected by the specialized tips of some nerve cells present in tissues and organs. These are called receptors. They are located in our sense organs like nose, tongue, skin, eye and inner ear.

Sensory receptors are of different types. Photoreceptors, phonoreceptors, olfactoreceptors, gustatoreceptors, thermoreceptors and so on. They detect light, sound, smell, taste, heat and cold respectively.

The above mentioned receptors initiate electrical impulses to be picked up by sensory nerves. This impulse travels from the dendrite to the cell body, and then along the axon to its end. Axon ending of one neuron are placed close to dendrites of the next neuron. This junction is called synapse or gap. As soon as the impulse reaches the end of neuron it sets off release of some chemical (Neurotransmitters). These chemicals cross the gap or synapse and start a similar electrical impulse in dendrite of next neuron. Finally, the impulse reaches a muscle or a gland.

9. If you happen to touch a hot object what would be your response ? With the help of well labelled diagram explain how this response happen.

Ans. If we happen to touch a hot object unknowingly, then our hand will be retraced back away from it. This happens as it is a never mediated, automatic, involuntary and a spontaneous response acting without consulting the will. Such a response is referred as a reflex action. The pathway taken by a stimulus to travel from receptor organ to effector organ is known as reflex arc.

10. Name the two components of central nervous system. How are they protected ? Name the component which is considered as highest coordinating centre of the body. Describe its three regions.

Ans. Brain and spinal cord are the two components of central nervous system.

Human brain is protected by a bony skull, also called as cranium. Internal to the skull it is covered from outside by three membranes called menings. In between the meninges there is a fluid called as cerebrospinal fluid. Bneath the membranes brain is subdivided into three major parts namely fore-brain, midbrain and hind brain.

Brain is considered as highest coordinating centre of the body.

Its three regions are given below :

(a) Fore-brain is the main thinking part of the brain. It has different regions or areas such as :

(i) Sensory area – It receives sensory impulses from various receptors.

(ii) Auditory area – It is concerned with hearing.

(iii) Gustatory area – It is concerned with taste.

(iv) Olfactory area –  Ii is concerned with smell.

(v)  Optic area – It is concerned with sight.

(vi) Association area – This area interprets various sensory informations and makes decision how to respond.

(vii) Motor area – Decisions made by association area is passed on to this area which control the movement of voluntary muscles.

(b) Midbrain comprises of four lobes. So it is also known as copra quadrigemina. Actions of involuntary muscles are controlled by the mid-brain and hind-brain.

(c) Hind-brain compirses of cerebellum, pons varolii and medulla oblongata. Cerebellum is the second largest part of brain that coordinated muscular activity of the body as well as maintaining body equilibrium or posture. Pons connects cerebellum and medulla oblongata and functions as a relay cenre among different parts of brain. It possesses pneumotaxix area of respiratory centre. Medulla oblongata lies bellow cerebellum and continues behind spinal cord. Involuntary actions like blood pressure, salivation and vomiting are controlld by the medulla in the hind-brain.

11. With the help of suitable example explain the terms phototropism, geotropism and chemotropism.

Ans. (i) The stimulus oriented movement of plant or plant part is called tropism. The direction of movement is related to the direction of stimulus. These movements are always growth oriented movements. They are of different types namely phototropism( Growth movement in response to light), hydrotropism ( water), geotropism (force of gravity), thigmotorpism (contact) and chemotropism (chemical).

(ii) Phototropism is a directional growth movement which occours in response to unidirectional exposure to light. The region of photoreception is shoot apex where auxin is produced. Auxin moves from illuminated region to the shaded region. This causes more growth on the dark side of stem causing it to bend towards the source of light. Movement of shoot towards light is called phototropism.

(iii) Roots are positively geotropic and negatively phototropic. Shoots are positively phototropic and negatively geotropic. Growth of pollen tube inside the style, ovary and ovule in response to the chemicals produced by them is an example of chemotropism.

12. (a) Define hormone. Write four characterstics of hormones in humans.

(b) Name the disorder caused by the following situation :

(i) Under secretion of growth hormone.

(ii) Over secretion of growth hormone.

(iii) Under secretion of insulin.

(iv) Deficiency of iodine.

Ans. (a) Hormones are chemical informational molecules that are required in minutes quantities and are directly poured in the blood stream. They act on a specific organ called target organ. So their site of production varies from site of action.

Their characteristics are :

(i) They are poured into blood stream.

(ii) Are generally proteinaceous or steroid.

(iii) Their secretion is regulated by feedback mechanism.

(iv) Their site of action and secretion is different.

(b) (i) Dwarfism

(ii) Gigantism

(iii) Diabetes

(iv) Goitre.

13. What is the significance of peripheral nervous system ? Name the components of this nervous system.

Ans. Peripheral nervous system comprises of nerves that directly arise from central nervous system connecting different parts of the body for voluntary control of the brain. It consists of cranial nerves and spinal nerves.

14. How do muscle cells respond to electrical impulses ?

Ans. Muscle cells have special proteins that change their shape and arrangement in the cell in response to electrical impulse. This leads to the excitation of the excitation of the muscle cells which then spreads over the whole muscle fibre. thereby causing it to shorten or contract.

15. List two primary functions of testosterone.

Ans. Testosterone is a male hormone that

(i) stimulates the development of male secondary sex organs at puberty.

(ii) also helps in development of male secondary sexual character like beard, moustache, deep voice and growth of bones.

Chapter 12 Electricity

Important Question

1.  What does an electric circuit mean ?

Ans. An electric circuit is a continuous and closed  path for flow of an electric current. If the electric circuit is complete, electric current can flow through the circuit. If the circuit is broken anywhere or switch of the circuit is turned off, the current  stops flowing.

2. Define the unit of current.

Ans. SI unit of electric current is ampere. Current is said to be 1 ampere (1 A), if 1 couloumb charge flows per second across a cross-section of a conductor.

3. Name a device that helps to maintain a potential difference across a conductor.

Ans. Potential difference across a conductor can be maintained by means of a battery consisting of one or more cells.

4. What is meant by saying that the potential difference between two points is 1 V ?

Ans. The potential difference between two points is said to be 1 volt, if 1 joule of work is to be done for moving a charge of 1 coulomb from one point to another.

5. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal ?

Ans. Coils of electric toasters and electric irons are made of an alloy (generally) nichrome) due to the following two reasons :

(i) Resistivity of an alloy is generally higher than that of pure metals, hence for a given resistance we need a coil of lesser length.

(ii) At high temperatures, an alloy does not oxidise (burn) readily. Hence, coil of an alloy has longer life.

6. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series ?

Ans. Advantages of connecting electrical devices in parallel with the battery are as follows :

(i) Voltage across each electrical device is same and the device is same and the device can take current as per its resistance.

(ii) Separate on/off switches can be applied across each device.

(iii) Total resistance in parallel circuit decreases, hence a greater current may be drawn from the cell.

(iv) If one electrical device is damaged, then other devices continue to work properly.

7. Why does the cord of an electric heater not glow while the heating element does ?

Ans. Cord and the electric heater are joined in series and carry same current when joined to a voltage source. As resistance of cord is extremely small as compared to that of heater element, hence, heat produced H = I²Rt is extremly small in cord but much larger in heater element. So, the heating element begins to glow but cord does not glow.

7. Explain the following :

(a) Why is the tungsten used almost exclusively for filament of electric lamps ?

(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rater than a pure metal ?

(c) Why is the series arrangement not used for domestic circuits ?

(d) How does the resistance of a wire vary with its area of cross -section ?

(e) Why are copper and aluminum wires usually employed for electricity transmission ?

Ans. (a) Tungsten is used exclusively for filament of electric lamps because its melting point is extremely high (3380 degree celcius).

(b) Conductors of electric heating devices are made of an alloy rater than a pure metal due to the following reasons :

(i) Resistivity of an alloy is generally higher than that of pure metals, hence for a given resistance we need a conductor of less length.

(ii) At high temperatures, an alloy does not oxidise (burn) readily. Hence, heating element prepared form an alloy has longer life.

(c) Series arrangement is not used for domestic circuits due to the following reasons :

(i) In series arrangement same current will flow through all the appliances, which is not required.

(ii) total resistance of domestic circuit will be sum of the resistances of all appliances and hence current drawn by the circuit will be less.

(iii) We cannot use independent on/off switches with individual appliances.

(iv) All appliances are to be used simultaneously even if we do not need them.

(d) Resistance (R) of a wire is inversely proportional to its cross-section area (A).

(e) Copper and aluminium wires are usually employed for electricity transmission because these are extremely good conductors having a low value of resistivity. Moreover, these are ductile and can be drawn in the form of fine wires.

8. Define potential difference between two points in a conductor.

Ans. Potential difference between two points A and B, in an electric field, is defined as the amount of work done in order to move unit positive charge from point B to point A. Thus,

9. What is meant by the statement “potential difference between points A and B in an electric field is 1 volt” ?

Ans. Amount of work done to bring 1 C charge from point B to point A in the electric field is 1 joule.

10. Which material is the best conductor ?

Ans. Silver

11. Define resistance of a conductor.

Ans. The electric resistance of a conductor is its property to oppose flow of electric charge through it and is measured by the potential difference being applied across the conductor so as to maintain the flow of one ampere current through it.

12. Keeping the potential difference constant, the resistance of an electric circuit is doubled. State the change in the reading of an ammeter connected in this circuit.

Ans. The reading of ammeter is reduced to one-half of its previous value.

13. The length of a wire is doubled and its cross-sectional area is also doubled. What is the change in its resistivity ?

Ans. There is no change because resistivity of a material depends only on its nature and is independent of its dimensions.

14. On what factors does the resistance of a conductor depend ?

Ans. Resistance of a conductor (i) is directly proportional to its length, (ii) inversely proportional to its cross-section area and depends on the material of the conductor. Resistance also depends on the temperature.

15. What is heating effect of electric current ?

Ans. When electric current is passed through a resistor, electrical energy is dissipated and appears as heat energy. This is known as the heating effect of electric current.

16. State joule’s law of heating.

Ans. As per joule’s law the heat produced in a resistor is (i) directly proportional to square of current flowing through it, (ii) directly proportional to resistance, and (iii) directly proportional to time. Mathematically,

Heat H = I²Rt

17. How many joules are equals to 1kWh ?

Ans. 3.6 x 10^6

18. Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use ?

Ans. 40 W lamp has a higher electrical resistance because R = V²/P.

19. Would you connect a fuse in series or in parallel to an electric circuit ?

Ans. In series of the electric circuit before appliances present in the circuit.

20. Why do electricians wear rubber gloves while working ?

Ans. Rubber is an electrical insulator. Hence electrician can work safely while working on an electric circuit without a risk of getting any electric shock.

21. what is heating effect of electric current ? Find an expression for amount of heat produced. Name some appliances based on heating effect of current.

Ans. When a current flows through a conducting wire, heat is developed and temperature of wire rises. It is known as the heating effect of electric current.

If V be the potential difference maintained across the ends of a wire then, by definition, the amount of work for flow of 1 C charge through the wire is V.

Therefor, Work done for flow of Q charge W = VQ = VIt

where I is the current flowing in time t. As V = IR

W = VIt = (IR)It = I²Rt

This is known as joule’s law of heating.

Incandescent lamps, electric iron, electric stove, toaster, geyser, electric room heater etc., are the appliances based on heating effect of electric current.

Chapter 13 Magnetic Effect of Electric Current

Important Questions

1. List the properties of magnetic lines of force.

Ans. Properties of magnetic lines of force are listed below :

(i) Outside a magnet, the magnetic field lines are directed from N-pole of magnet to the S-pole. However, inside a magnet, the field lines are directed from S-pole to N-pole. Thus, magnetic lines are closed curves.

(ii) A magnetic field line always points in the direction of magnetic field.

(iii) The relative strength of magnetic field lines is given by degree of closeness of the field lines. The magnetic field is stronger in the region where the lines are crowded.

(iv) No two magnetic field lines can ever intersect with each other.

2. Why don’t two magnetic lines of force intersect each other ?

Ans. No two magnetic field lines can ever intersect each other. If they do, then it would mean that at the point of intersection there are two directions of magnetic field, which is not possible.

3. A current -carrying conductor is placed in a magnetic field. Now answer the following :

(i) List the factors on which the magnitude of force experienced by conductor depends.

(ii) When is the magnitude of this force maximum ?

(iii) State the rule which helps in finding the direction of motion of conductor.

(iv) If initially this force was acting from right to left, how will the direction of force change if :

(a) direction of magnetic field is reversed ?

(b) direction of current is reversed ?

Ans. (i) The magnitude of force experienced by current-carrying conductor when placed in a magnetic field depends on (a) current flowing(I), (b) length of conductor (l), (c) the strength of magnetic field (B) , and (d) orientation of conductor in magnetic field.

(ii) Magnitude of force is maximum when current-carrying conductor is placed at right angles to the direction of magnetic field.

(iii) Fleming’s left-hand rule states that stretch the forefinger, the central finger and the thumb of your left-hand in mutually perpendicular directions. If the forefinger shows the direction of the magnetic field and the central finger that of the current, then the thumb will point towards the direction of motion of the conductor.

(iv) (a) Direction of force is reversed that is now the force acts from left to right.

(b) Direction of force is reversed that is now the force acts from left to right.

4. Explain the activity to show that a current-carrying conductor experiences a force when placed in a magnetic field.

Ans. A current-carrying conductor experiences a magnetic force due to a magnetic field. The force is maximum when the conductor is placed perpendicular to the direction of magnetic field. To demonstrate the force we perform the following experiment :

Experiment : Take a small sized aluminium rod AB of length about 5 cm. Suspend the rod AB horizontally form a rigid stand using two connecting wires.

Place a strong horse-shoe magnet NS is such a way that the rod AB lies between the poles of the magnet. Let the north pole N of magnet lies below the rod and the south pole S lies directed in vertically upward direction is present.

Complete the electrical circuit of aluminium rod AB by connecting it in series with a battery, key K and a variable resistance.

Put the plug in key K so that an electric current begins to flow through the aluminium rod from end B to end A. We observe that on passing current the rod AB is displaced towards the left. It shows that the aluminium rod is experiencing a mechanical force due to which it is being deflected. Direction of deflection is given by Fleming’s left hand rule.

Effect of change in direction of current : Reverse the connections of battery so that on applying plug in key K, current flows in the aluminium rod form A to B. We now find that the rod AB is deflected towards the right. Thus, by reversing the direction of current, direction of force is also reversed. It is in accordance with Fleming’s left-hand rule.

Effect of change in direction of magnetic field : Now reverse the direction of magnetic field to vertically downward direction. For this purpose suspend, the horse-shoe magnet in such a way that N-pole of magnet lies above the aluminum rod AB and S-pole of magnet lies below the rod. If now current in aluminium rod is flown from B to A, the rod is deflected towards right. If current in the rod is flowing from A to B, then the rod is deflected towards left. It shows that direction of deflection is reversed on reversing the direction of magnetic field.

5. One of the major causes of fire in office buildings is short-circuiting. List three reasons which may lead to short-circuiting. How can it be prevented ?

Ans. Three possible reasons of short-circuiting of an electrical circuit are as follows :

(i) The insulation of electrical wirings is damaged.

(ii) The electrical appliance used in the circuit is defective.

(iii) An appliance of higher power rating is being run on an electrical line of lower power rating.

short-circuiting can be prevented by the use of electrical fuse of appropriate capacity.

6. Describe four important features of domestic electric supply lines.

Ans. Important features of domestic electric supply lines are as given below :

(i)  Different circuits and different appliances in each circuit are connected in parallel.

(ii) Each appliance is provided with an independent on/off switch which is always joined to the live wire.

(iii) Two separate circuits are used, one of 15 A for appliances with higher power ratings and another of 5 A for bulbs, tubes etc.

(iv) Electric fuses of appropriate capacities are used ahead of each electric circuit as a safety measure. Moreover, proper earthing must be ensured.

7. Describe an activity to explain how a moving magnet can be used to generate electric current in a coil.

Ans. Take a coil AB of insulated copper wire having a number of turns. Connect the ends of coil to a sensitive galvanometer G. Now take a bar magnet NS and rapidly bring the magnet towards the end B of coil . The galvanometer gives momentary deflection in on direction. Now take the magnet away from the coil, the galvanometer again gives momentary deflection but in the opposite direction. It clearly shows that motion of magnet induces, a current in the coil.

Again keep the magnet fixed and gently move the coil AB either towards the magnet of away from the magnet. We get deflection in galvanometer even now. Thus, an induced current is produced in a coil whenever there is relative motion between the coil and the magnet. This phenomenon is known as the electromagnetic induction.

8. A metallic conductor is suspended perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards left when a current is passed through it. What will happen to the displacement of the conductor if the :

(i) current through it is increased ?

(ii) horse-shoe magnet is replaced by another stronger horse-shoe magnet ?

(iii) direction of current through it is reversed ?

Ans. (i) On increasing the current flowing through metallic conductor, the force experienced by it is proportionately increased because F is directly proportional to l

(ii) On using a stronger horse-shoe magnet the magnetic force increases because F is directly proportional to B.

(iii) On reversing the direction of current the direction of force is reversed and conductor is displaced towards right instead of left direction.

9. What are magnetic field lines? How is the direction of magnetic field at a point determined ? Mention two important properties of magnetic field lines.

Ans. Magnetic field lines are used to represent a magnetic field. A field line is the path along which the north pole of a small compass tends to move. The direction of the magnetic field at a point is given by the direction in which north pole of compass placed at that point would take.

10. What happen if a domestic electric circuit is short-circuited ?

Ans. As a result of short-circuiting, the resistance of the circuit decreases to a very small value and consequently the current increases enormously. It results in heating the live wires and producing a spark at the place of short circuit, which may even cause fine in the building.

11. What precautions should be taken to avoid the overlaoding of domestic electric circuits ?

Ans. Following precautions should be taken to avoid the overloading of domestic electric circuits :
(i) too many electrical appliances should not be operated using a single socket.
(ii) Too many large power rating appliances should not be switched on at a time.

12. What is short-circuiting ? What is its possible cause ?

Ans. Short-circuiting means that the two wires, live and neutral, of the domestic electric circuit have come in contact with each other. Short-circuiting may take place either due to their insulations having been damaged or due to a fauld in the appliances.

13. What is the role of fuse, used in series with any electrical appliance ? Why should a fuse with defined rating not be replaced by one with a larger rating ?

Ans. The fuse is a safety device used to prevent any damage to an electrical appliance either due to short-circuiting or overloading of the electrical circuit.IF a fuse, with defined rating, is replaced by one with a larger rating then the fuse wire will nor burn even when a current even greater amount than the safe limit is flowing. As a result the electrical appliances will be damaged.

14. What is the usual colour code followed for connecting live, neutral and earth wires ? Why is it important ?

Ans. As per usual colour code followed the live wire is of red coloured insulation, neutral wire of black coloured insulation and earth wire is of green coloured insulation. If the colour code is followed then any person would identify the correct connecting wire and would be able to handle them properly.

15. Mention the provision of two different current ratings in our domestic circuits. Explain, with reason, the advantage of such a provision.

Ans. In our domestic circuits provision is made for two different current ratings :
(i) a rating of 5 A for bulbs, tubes, CFL’s and fans etc.
(ii) a rating of 15 A for electric iron, gyser, refrigerator etc
Advantage of this provision is that we may use fitting and line wire of appropriate power rating for appliances.

16. Distinguish between a direct current and alternating current.

Ans. Direct current(D.C.)
(i) Direct current always flows in one direction only
(ii) The magnitude of current may or may not remain constant
(iii) Current obtained from a battery and D.C generator is D.C.

Alternating Current (A.C.)
(i) Alternating current reverses its direction periodicly.
(ii) Magnitude of current continuously changes with time.
(iii) Current obtained from an A.C. generator and current in our domestic circuit are A.C.

17. Distinguish between Electric Motor and Electric Generator

Ans. Electric Motor
(i) It is a device which converts electrical energy into mechanical energy.
(ii) It works on the principle of Fleming’s left-hand rule.

Electric Generator
(i) It is a device which converts mechanical energy into electrical energy.
(ii) It works on the principle of Fleming’s right-hand rule.

18. State two ways by which the strngth of an electromagnet can be increased.

Ans. the strength of an electromagnet can be increased by
(i) increasing the number of turns of windings of the solenoid coil wrapped around the electromagnet.
(ii) increasing the amout of electric current flowing through the coil.

Chapter 14 Sources of Energy

Important Questions

1. What is good source of energy ?

Ans. A good source of energy should have the following qualities :

(i) It should be easily available.

(ii) It should do a large amount of work per unit volume/mass.

(iii) It should be easy to store and transport.

(iv) It should be economical.

(v) It should not cause environmental pollution.

2. What is a good fuel ?

Ans. A good fuel is that which releases more heat on burning, is easily available at an economic rate and does not produce smoke.

3. What are the disadvantages of fossil fuels ?

Ans. There are following disadvantages of fossil fuels like coal and petroleum :

(i) Burning of coal or petroleum causes air pollution.

(ii) Acidic oxides like oxides of carbon, nitrogen and sulphur are released on burning fossil fuels. These oxides lead to acid rains, which adversely affect out water and soil resources.

(iii) Carbon dioxide gas also causes greenhouse effect in atmosphere.

(iv) Fossil fuels are non-renewable sources of energy.

4. What are the limitations of the energy that can be obtained from the oceans ?

Ans. Energy from the oceans can be obtained in the form of tidal energy, wave energy and ocean thermal energy. But these energy sources suffer from the following limitations :

(i) There are very few locations where dams to utilize tidal energy can be built.

(ii) Cost of installation of power houses is extremely high and efficiency of plants is comparatively small.

(iii) Power plants built in oceans or at sea-shores will need high continuous maintenance as chance of corrosion are extremely high.

5. What is geothermal energy ?

Ans. Geothermal energy is the heat energy present inside earth in certain regions called hot spots. Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upwards and are trapped in hot spots. When underground water comes in contact with the hot spot, steam is generated. This steam is routed through a pipe to a turbine and used to generate electricity.

6. What is fuel ?

Ans. Fuel is that which produces heat energy on burning e.g., firewood, charcoal, coal, petroleum, cooking gas etc.

7. Why is the solar cooker box covered with a plane glass plate ?

Ans. The glass plate allows solar radiation to pass through it but the heat radiation form inside are not allowed to escape by the glass plate. Thus, it helps in maintaining the temperature inside the cooker high.

8. Identify the part of a solar cooker that produces greenhouse effect.

Ans. The plan glass plate cover.

9. What is the chief source of wind energy ?

Ans. Sun is the chief source of energy. Wind is caused by unequal heating of land mass and water bodies by solar radiation.

10. How does construction of dams across the river get linked with the production of greenhouse gases ?

Ans. The vegetation of submerged areas of forests rots under anaerobic conditions and gives rise to methane, which is a greenhouse gas.

11. Write the percentage of methane in bio-gas ?

Ans. 75% of bio-gas is methane.

12. List two nutrients that the slurry left behind in a bio-gas plant contains.

Ans. It serves as an excellent manure because it is rich in nitrogen and phosphorus.

13. Define the process of nuclear fission ?

Ans. Splitting up of a nucleus of uranium, when bombarded by neutrons, into two lighter nuclei along with release of a large amount of energy is called nuclear fission.

14. Explain, why fossil fuels are classified as non-renewable sources of energy.

Ans. Fossil fuels were formed due to certain very slow changes occurring inside the earth under special circumstances spread over millions of years. Since these conditions are not prevailing now, it is not possible to replenish the amount of fossil fuels being consumed. Hence, these are classified as non-renewable sources of energy.

15. Name the process for obtaining charcoal from wood. What are the advantages and disadvantages of burning charcoal over wood ?

Ans. Charcoal is obtained by destructive distillation of wood.

Advantages : (i) It burns easily producing no smoke. (ii) It gives twice as much heat as is obtained by burning the same mass of wood.

Disadvantages : It is expensive. One kilogram of wood gives only 1/4 kg of charcoal by destructive distillation.

16. State any three limitations of harnessing nuclear energy.

Ans. Three main limitations of harnessing nuclear energy are as follows :

(i) The most important problem is the storage and disposal of spent or used fuel because it is highly radioactive. Improper nuclear waste storage and disposal may lead to environmental contamination.

(ii) There is a risk of accidental leakage of nuclear radiation from the nuclear reactor.

(iii) Cost of installation of a nuclear power plant is very high.

17. Burning of fossil fuels causes lots of air pollution. Generally these fossil fuels are used in our vehicles.

(i) As an aware citizen, list two ways to reduce air pollution caused due to vehicles.

(ii) Write two harmful effects other than air pollution, that are caused due to burning of fossil fuels.

Ans. (i) Two ways to reduce air pollution caused due to vehicles are as follows :

(a) The petrol used should be free of lead and sulphur impurities because oxides of these elements are toxic and cause much air pollution.

(b) Vehicles using diesel should be replaced by vehicles using CNG as fuel.

(ii) Two harmful effects, other than air pollution, caused due to burning of fossil fuels are as follows :

(a) Burning of fossil fuels produce oxides of nitrogen and sulphur. These gases are acidic in nature and lead to acid rain which adversely affects our water and soil resources.

(b) Burning of fossil fuels produce carbon dioxide, which is a greenhouse gas and leads to global warming causing a lot of environmental and ecological problems.

18. Name two semiconductor used in solar cell. What is solar cell panel ? State two main advantages of solar panel.

Ans. Silicon and gallium are two semiconductors commonly used in solar cell. A solar panel is an arrangement in which a large number of solar cells are combined so that. it can deliver enough electricity for practical use.

Solar panels have following advantages :

(i) They have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device.

(ii) These can be set up in remote and inaccessible hamlets or very sparsely populated areas where laying of a power transmission line is not commercially viable.

19. How can one say that Sun is the main source of energy on the earth ?

Ans. Solar energy manifestats itself in many forms through many processes both biological and physical. plants utilise solar energy for photosynthesis. The solar energy trapped by land and water bodies brings about many physical changes resulting in wind, storm, ocean waves etc. Also fossil fuels e.g., coalm natural gas, petrol etc. have been formed due to very slow changes which occurred millions of years ago and were related to solar energy. Energy of bio-gas etc., is also derived from solar energy.

20. What is bio-mass ? Explain the principle and working of a bio-gas plant using a labelled diagram.

Ans. Animal dung, crop residue, vegetable waste and sewage constitute the bio-mass. A bio gas plant as shown in NCERT book . In a bio-gas plant slurry of animal dung or other types of bio-waste and water is made in the mixing tank and then fed into the digester. The digester is usually a closed underground tank. In digester, the action of micro-organisms decomposes the complex compounds of the bio-mass in the slurry. In the presence of water anaerobic micro-organisms degrade the bio–mass in the digester. An anaerobic micro-organisms do not require oxygen, the digester is designed like a sealed chamber. The compete degradation process takes few days, during which bio-gases are produced. Noe the bio-gas can be supplied to consumers through pipes. Periodically the slurry, that is left behind in the digester, is removes and it serves as an excellent manure.

21. Explain, how does a hydro power plant produce electricity.

Ans. A hydro power plant converts the potential energy of stored water into electricity.

To produce hydro power electricity, a high rise dam is constructed at a suitable place on the river to obstruct the flow of water and thereby collect water in a large sized reservoir. Due to rise of water level, the kinetic energy of flowing water is transformed into potential energy of stored water.

The water from the high level in the dam is carried through sluice gates and pipes to the turbine of electric generator, which is fitted at the bottom of the dam. Due to flowing water, turbine is rotated at a fast rate and electricity is produced.

Chapter 15 Our Environment

Important Question

1.Mention one negative effect of our affluent life style on the environment.

Ans. Our activity in our affluent life style pollute the environment.

2. Why has there been huge hue and cry against the use of CFC’s ?

Ans. CFC’s on reaching the upper layer of atmosphere causes ozone layer depletion and allows UV rays to enter earth’s atmosphere.

3. Name the radiations from the sun that are absorbed by ozone layer. Mention one harmful effect caused by them.

Ans. Ultraviolet radiations are absorbed by ozone layer. Ultravoilet radiations cause skin cancer.

4. What is meant by non-biodegradable waste ? Identify biodegradable waste from the following :

Empty packet of chips, empty bottle of mineral water, empty paper box of sweets, empty tin of a cold drink.

Ans. Substances that do not breakdown by biological process are called non-biodegradable waste. Empty paper box of sweets is biodegradable.

5. State two methods to get rid of non-biodegradable wastes.

Ans. We should carry cloth bags when we go for shopping. Non-biodegradable waste should be collected separately and sent for recycling.

6. Why is ozone layer getting depleted at the higher levels of the atmosphere?

Ans. Depletion of ozone layer is due to the use of chlorofluorocarbons which are used as refrigerants and in fire extinguishers.

7. State the function of digestive enzymes.

Ans. Digestive enzymes break down the food into small and water soluble soluble molecules.

8. Where do plants get each of the raw materials required for photosynthesis ?

Ans. Plants get carbon dioxide from the atmosphere and nitrogen from the soil for photosynthesis.

9. What is meant by the term Environment ?

Ans. Environment is the sum total of all external conditions and influences that affect the life and development of an organism. Environment includes all the physical or abiotic and biological or biotic factors.

10. Name any two non-biodegradable wastes.

Ans. DDT and polythene bags.

11. In a certain study conducted on occurrence of DDT along food chains in an ecosystem, the concentration of DDT in grass was found to be 0.5 ppm in sleep it was 2 ppm and in man it was 10 ppm. Why was the concentration of DDT maximum in case of man ?

Ans. DDT is non-biodegradable. It accumulates at each tropic level. As man is positioned at the highest tropic level, there is maximum accumulation of DDT in man. This phenomenon is called biological magnification.

12. Explain how does making of kulhads affect our environment ?

Ans. A lot of soil is needed for making kulhads. It results in large scale pepletion of top fertile soil. Moreover, disposal of used kulhads is not so easy.

13. Define a food web. State its significance for ecosystem.

Ans. A system of food chains which are interconnected between various organisms is called a food web. The significance of food wen is in the maintenance of ecological balance based upon interdependence of different organisms.

14. State one important function of ozone layer in the atmosphere. How is it formed there ? Which compounds are responsible for the depletion of ozone layer ? How do these compounds enter into the atmosphere ?

Ans. Ozone layer prevents harmful ultraviolet radiations to reach earth’s atmosphere. Ozone is formed at the higher level of atmosphere by the action of UV radiations on O2 molecule. HIgh energy UV radiations split apart some oxygen to form ozone molecules as shown by the following equations :

O2 —— O + O

O2  +  O —– O3

Chlorofluorocarbons are responsible for the depletion of ozone layer. These compounds which are used in refrigerators and fire extinguishers get leaked during manufacture or repair and go up high into the atmosphere.

15. (a)What is an ecosystem ? List its two main components.

(b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain

Ans.(a) A self-sustaining functional unit consisting of living and non-living components is called ecosystem.

Components : Biotic components like plants and animals. Non-biotic components like soil, wind, light etc.

(b) A pond is a complete, natural and self-sustaining ecosystem whereas an aquarium is an artificial and incomplete ecosystem, therefore it needs regular cleaning for proper running.

16. “Damage to the ozone layer is a cause of concern” Justify this statement. Suggest any two steps to limit this damage.

Ans. Ozone layer protects the earth from the harmful effects of ultraviolet radiations. Damage to ozone layer will result in UV rays reaching the earth and cause skin cancer, cataract and damage to immune system.

Steps to limit the damage :

(i) Minimise the use of CFC.

(ii) Freeze CFC production at 1986 level as per UNEP recommendation.

(iii) Device chemicals in place of CFC’s to perform their functions.

17. Why are bacteria and fungi called decomposers ? List any two advantages of decomposers ?

Ans. Bacteria and fungi are called decomposers because they degrade and decomposes dead remains of plants and animals into simpler inorganic susbtance which go into the soil as nutrients.

Advantages : Decomposers degrade garbage and organic wastes which would otherwise cause environment problem. It prevents foul smell and checks spread of diseases.

Decomposers recycle the nutrients through biogeochemical cycle.

18. What is ten percent law ?

Ans. Energy available at each successive trophic level of food chain is ten percent of that at the previous level.