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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