SCIENCE Ch. 13: Magnetism WORKBOOK QUESTION ANSWER

 Ch. 13: Magnetism 

1. Choose the correct option. 

a) The meaning of lodestone is 

i) magnetite ii) leading stone 

iii) natural magnet iv) temporary magnets 

Ans: B- leading stone  

b) Which of the following is attracted by a magnet? 

i) Silver ii) Pieces of paper  

iii) Hair iv) Cobalt 

Ans: D - Cobalt 

c) Which of the following is a natural magnet?  

i) Cobalt ii) Magnetite 

iii) Nickel iv) Natural coal 

Ans: B Magnetite  

2. Assertion-Reasoning Questions.  

In the following questions, two statements are given- one labelled Assertion (A)  and the other labelled Reason (R). Read the statements carefully and choose  the correct alternative (A), (B), (C) and (D) as given below. 

(A) Both A and R are true and R is the correct explanation of the assertion. (B) Both A and R are true but R is not the correct explanation of the assertion. (C) A is true but R is false. 

(D) A is false but R is true. 

a) Assertion: Magnetic poles always exist in pairs. 

Reason: Artificial magnets are obtained through an artificial process. Ans: (B) Both A and R are true but R is not the correct explanation of the  assertion. 

b) Assertion: A compass is used by navigators and pilots to find directions.  Reason: A freely suspended magnet always aligns in the north-south  direction.  

Ans: (A) Both A and R are true and R is the correct explanation of the assertion.

3. Answer the following questions in brief. (4 to 5 lines) 

a) What are non–magnetic materials? 

i. Materials which are not attracted by magnets are called non-magnetic  materials.  

ii. Stone, glass, water, rubber, wood, aluminium, grass, are non magnetic materials. 

b) What would you observe if two magnets are brought close to each other?  i. The magnets will repel each other if the same magnetic poles (like  north-north or south-south) are brought close to each other.  ii. The magnets will attract each other if the same magnetic poles (unlike  poles north-south or south-north) are brought close to each other.  

c) What happens to the poles of a magnet if it breaks into two pieces?  i. When a bar magnet breaks into two pieces, each broken piece will  have a north pole and a south pole of its own.  

d) How can one identify the North Pole and South pole of a magnet, if there is  no indication on it? 

i. First hang the bar magnet freely with the help of a light thread. ii. Then allow the magnet come to rest on its own. Now the end of the  magnet which points to the north is the North Pole and the end which  points to the south is the south pole. 

4. Answer the following questions in detail. (5 to 6 lines) 

a) Describe the properties of a magnet. 

i. Property of Attraction - A magnet attracts metals such as iron,  cobalt, nickel and mixtures of these metals. 

ii. Property of Direction - A freely suspended magnet always rests in  the north-south direction. 

iii. Property of Attraction and Repulsion - Unlike poles of a magnet  attract each other, whereas like poles repel each other. 

iv. Magnetic poles always exist in pairs. 

b) Explain the construction of a magnetic compass.  

i. A magnetic compass consists of a magnetised needle pivoted  inside a small box with a glass cover on it.  

ii. The magnetic compass has a dial on which directions are marked. iii. The north pole of a magnetised needle is normally painted in red  colour for easy identification.  

iv. The magnetised needle when at rest indicates the north-south  direction.

c) Why is repulsion a true test for verification of a magnet? 

i. A magnet can attract magnets as well as magnetic materials.  ii. So, if the criterion of attraction is used to test magnetism of an  object, then not only magnets, but also all magnetic materials  would pass the test. 

iii. On the other hand, a magnet can repel only other magnets if two  like poles of magnets are brought together. 

iv. Therefore, if an object is repelled by a magnet, then that object  is certainly a magnet. 

5. Write short notes on the following. (3 to 4 lines) 

a) Artificial magnets 

i. Magnets which are obtained through an artificial process are  called artificial magnets.  

ii. These types of magnets are made with hard steel or special alloys  of iron.  

iii. These magnets can be made in different shapes and sizes for  various uses.  

iv. For example, ring shaped magnets are used in speakers. 

b) Poles of a magnet 

i. Each magnet has two magnetic poles, irrespective of the shape.  These poles are called the North Pole and the South Pole. ii. The end of a freely suspended magnet, which points towards the  geographical north, is called the North Pole. It is also referred to  as north seeking pole. 

iii. The end of a freely suspended magnet, which points towards the  geographical south, is called the South Pole. It is also referred to  as south seeking pole. 

iv. The most important fact about magnetic poles is that they always  exist in pairs. 

6. Observe the picture and answer the questions that follow: Iron Filings

Ch. 13: Magnetism 

a) Identify the type of magnet shown in the picture. 

Ans.: Bar magnet. 

b) What can you infer about the strength of different parts of the magnet from the  picture? Justify your answer.  

Ans.: The strength of the magnet is greatest at the poles and weakest at the  centre.  

This can be inferred a larger concentration of iron fillings are present at the  ends of the bar magnet as compared to the centre of the magnet.  

7. Suppose you are travelling to Antarctica (located at the South Pole) by a ship. The  structure of the ship is good but its engine is old and out of order. In order to reach the  destination someone gives a suggestion let’s magnetise the ship then the south  seeking pole will naturally take us to the Antarctica.  

Formulate an argument that will prove that this suggestion will not work.  Ans.: 

i. A magnetised ship not only acquires a South Pole but also a  North Pole. 

ii. The Earth’s magnetic field attracts both poles of the ship with  equal magnitude.  

7. Higher Order Thinking Skills (HOTS) 

 Identify the magnetic poles A and B from the following diagram. 

Ans.: A and B both are North poles 

8. Complete the following crossword puzzle with the help of given clues: Horizontal Vertical 

3. only natural magnet 

4. man-made magnet 

5. the strength of a magnet is highest at its 8. a magnet demagnetised in short period of  time 

9. material like cobalt, iron, etc. 

1. Like poles 

2. magnets lose their magnetic properties 6. the Earth behaves as a huge  

__________________ magnet 

7. a device is used to find out direction

Ch. 13: Magnetism 

Ans.: Horizontal                         Vertical 

3. magnetite                                                         1. repel 

4. artificial                                                             2. demagnetisation 

5. poles                                                                 6. bar 

8. temporary                                                             7. compass 

9. magnetic 

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SCIENCE CHAP 14. Air Around Us WORKBOOK QUESTION ANSWER

 Objective type questions

14. Air Around Us 

1. Choose the correct option. 

a) The amount of nitrogen present in the atmosphere is __________. i) 20% ii) 78% 

iii) 16% iv) 0.03% 

ans: 78% 

b) _________________ gas is used in extinguishing fires. 

i) Oxygen ii) Hydrogen 

iii) Carbon dioxide iv) Nitrogen 

ans: Carbon dioxide 

c) _____________ mark the beginning of the oxygen cycle. i) Bacteria ii) Land animals iii) Sea animals iv) Plants 

ans: Plants 

2. Name the following: 

a) The excessive cutting of trees. 

ans: Deforestation 

b) The envelope of air surrounding the earth. 

ans: Atmosphere 

c) The method used for separation of husk from grains using wind. ans: Winnowing 

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3. State whether the following statements are true or false.  

a) Windmills are used to draw water from tube wells. 

ans: True 

b) The amount of water vapour present in the atmosphere is fixed. ans: False 

c) Nitrogen supports combustion. 

ans: False 

4. Assertion-reasoning type questions: 

In following questions, the Assertion and Reason have been put forward. Read the  statements carefully and choose the correct alternative from the following: (A) Both Assertion and Reason are true and the Reason is a correct explanation  of the Assertion. 

(B) Both Assertion and Reason are true but Reason is not a correct explanation  of the Assertion. 

(C) Assertion is true but the Reason is false. 

(D) Both Assertion and Reason are false. 

a) Assertion: The ruler stoops to one side, when one of the balloons tied at  the two ends of a ruler is punctured. 

Reason: Air is invisible. 

ans: (B) Both Assertion and Reason are true but Reason is not a correct  explanation of the Assertion. 

b) Assertion: Use of alternate sources of energy such as wind energy and  solar energy should be encouraged. 

Reason: Alternate sources of energy do not cause air pollution. 

ans: (A) Both Assertion and Reason are true and the Reason is a correct  explanation of the Assertion.

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Theory type questions

5. Define the following: 

a) Oxygen cycle 

ans: The cycle in nature in which the oxygen is consumed for respiration  and is released during the process of photosynthesis is called oxygen  cycle. 

b) Air pollution 

ans: The presence of undesirable substances in the air that cause harmful  effects is known as air pollution. 

6. Answer the following in brief. 

a) What is the significance of hair and mucus present inside the nose of  human beings? 

ans: They prevent the dust particles from entering our lungs. 

b) Which harmful gases are produced by burning of fuels in automobiles and  factories? 

ans: Harmful gases such as carbon monoxide, oxides of nitrogen and  hydrogen sulphide produced by burning of fuels in automobiles and  factories. 

c) Give one use of nitrogen. 

ans: It is used in the manufacture of fertilisers. 

7. Give reasons for the following statements. 

a) It is difficult to breathe at higher altitudes. 

ans: As the layer of air is very thin at higher altitudes. 

b) If a burning candle is covered using a tumbler, it goes off in sometime. ans: Oxygen is necessary for burning. The candle goes off as it uses up all  

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the oxygen present inside the glass. 

Picture based question

8. Observe the given picture and answer the questions that follow.

a) Why do you see bubbles escaping from the bottle? 

ans: The bottle had air which escaped on tilting the bottle in the form of  bubbles. 

b) What can you conclude from the above activity? 

ans: Air occupies space. 

Real life learning 

9. There is a chemical factory in your locality that emits lots of gases into the atmosphere. The harmful effects of this are seen on people living in nearby areas. Suggest any one step that the chemical factory can follow to reduce air pollution. ans: The chemical factory should install long chimneys so that the harmful  gases are released high up in the air and away from humans. 

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Fun based questions

10. Fill in the missing letters appropriately. 

1. The process of formation of water vapour from water by heating. E V A P O R A T I O N 

2. The harmful substances present in the air.  

P O L L U T A N T S 

HOTS 

11. Higher Order Thinking Skills (HOTS) 

What will happen if all plants were to vanish from the surface of the earth? Justify  your answer. 

ans: ∙ As the plants mark the beginning of the oxygen cycle, no plants means no  photosynthesis. 

∙ No photosynthesis means no oxygen for respiration and the very life on  the earth will come to an end. 

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SCIENCE CHAP 12 ELECTRICITY & CIRCUITS WORKBOOK QUES - ANSWER

                                                         Ch 12. Electricity and Circuits 

1. Choose the correct option. (Ap/U) 

a) Which of the following materials allow an electric current to pass through  them? 

i) Cotton ii) Copper  

iii) Wood iv) Plastic  

Ans: Copper 

b) A dry cell consists of zinc metal that acts as the__________ terminal and a  carbon rod that acts as the ___________ terminal of the cell. 

i) negative, negative ii) positive, negative 

iii) negative, positive iv) negative, negative  Ans: negative, positive 

c) _________ acts as the negative terminal of a bulb. 

i) bottom of the bulb ii) Ammonium chloride iii) metal case iv) Manganese dioxide Ans: metal case 

2. State true or false: (U) 

a) Electricity is a form of energy resulting from the existence of charged  particles. 

Ans: True 

b) We should use water to extinguish a fire in electric wires.  

Ans: False 

c) Electrons do not revolve around the nucleus in fixed orbits. 

False 

3. Give an example for each of the following. (Ap) 

a) Natural resources used to generate electricity 

Ans: Sun, wind, water and nuclear energy

b) Secondary cells 

Ans: Car batteries 

4. In the following questions, two statements are given- one labelled  Assertion (A) and the other labelled Reason (R). Read the statements  carefully and choose the correct alternative (A), (B), (C) and (D) as given  below. (An) 

(A) Both A and R are true and R is the correct explanation of the assertion. (B) Both A and R are true but R is not the correct explanation of the  assertion. 

(C) A is true but R is false. 

(D) A is false but R is true. 

a) Assertion : In an electric bulb, the filament is made up tungsten. Reason: Tungsten does not melt even when the filament glows at a very high  temperature. 

(A) Both A and R are true and R is the correct explanation of the  assertion. 

b) Assertion: If you notice a spark in a switch, put it off immediately with the  help of a metal stick. 

Reason: Metal is a good conductor of electricity. 

(D) A is false but R is true. 

5. Explain the following: (U) 

a) Nucleus  

Ans: Protons and neutrons form the central part of the atom called the  nucleus. 

b) Conductors  

Ans: The materials that allow an electric current to flow through them.  

6. Answer the following questions in brief. (R/U) 

a) What is an electric cell? Name the two types of electric cells. Ans: Electric cell is a device that generates an electric current. It converts  chemical energy into electrical energy. Electric cells are of various shapes  and sizes.  

Primary cell/dry cell and secondary cell/lead-acid accumulators

b) Name the scientist who has discovered electricity. Why is electricity  important?  

Ans: Benjamin Franklin 

All gadgets and devices like computers, televisions, washing machines,  refrigerators, fans, air conditioners, etc. which make our lives  comfortable work on electricity. 

7. State the function of each of the following: (R) 

a) Electric switch  

Ans: An electric switch is used to open or close an electric circuit. 

b) The plastic coating of electric wires 

Ans: Protect us from getting electric shocks. 

8. You are given two dry cells, switch and bulb. Draw an electric torch showing  two dry cells. Which component of the torch is responsible for the flow of  electric current? (C) 

Ans: 

The electric cells inside the torch are responsible for the flow of electric  current. 

9. Observe the picture and answer the questions that follow. (Ap) (a) (b) (c)

In which of the following arrangements will the bulb? Give Reason. (b) 

In (b), the bulb will glow as the circuit is complete. 

10. Aditya performed an experiment to observe the flow of electric current  through an electric bulb. The bulb is connected to the cells in two different  ways as shown in (a) and (b). Which of these is the correct way to connect the  bulb? Why? (U) 

(a) (b)

(b) To complete the circuit and for the flow of current in the electric  circuit, the arrangement of cells are in correct order. 

11. Who am I ? (U) 

1. I am displayed on electric poles and transformers, warning you to stay away  from me. 

Danger sign 

2. I am a continuous flow of electrons 

Electric current 

3. I am round in shape. I provide energy to electronic devices like wrist watches  and pocket calculators. 

Button cell 

12. Higher Order Thinking Skills (HOTS) (U) 

Seema was testing electric circuits. She tested two conditions as given in fig A  and fig B. 

REFER TO TEXTBOOK FOR DRAWING

(a) What will be the direction of flow of current in fig A and fig B? fig A – P to Q 

fig B – Q to P 

(b) In which of the above figures will the bulb glow?  

Both fig A and fig B 

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