Chapter 13: Fun with magnets (Solutions)Posted on : 14-06-2018 Posted by : Admin

1. Fill up the blanks in the following:

(i) Artificial magnets are made in different shapes such as Horse shoe shape, ring shaped and ball ended magnet.

(ii) The Materials which are attracted towards a magnet are called magnetic materials.

(iii) Paper is not a magnetic material.

(iv) In olden days, sailors used to find direction by suspending a piece of magnet.

(v) A magnet always has two poles.

2. State which of the following statements are True and False

(a) A cylindrical magnet has only one pole. (False)

(b) Artificial magnets were discovered in Greece. (False)

(c) Similar poles of a magnet repel each other. (True)

(d) Maximum iron filings stick in the middle of a bar magnet when it is brought near them. (False)

(e) Bar magnets always point towards North-South direction. (True)

(f) A compass can be used to find East-West direction at any place. (True)

(g) Rubber is a magnetic material. (False)

3. It was observed that a pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic. Name a material that might have been used to make some part of it.

Answer: The blade of pencil sharpener is made of iron which is a magnetic material. Since magnets can attract objects made of magnetic materials, a pencil sharpener gets attracted towards both poles of a magnet.

4. Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting action between them for each situation. Fill in the blanks.

Answer: The following are the resulting actions of the magnet for different position when one pole of a magnet is placed near other. This is due to the fact that like poles repel and opposite poles of a magnet attract each other.

Column I Column II
N-N Repulsion
N-S Attraction
S-N Attraction
S-S Repulsion

5. Write any two properties of a magnet.

Answer: The following are two properties of a magnet:

(i) Magnets attract objects made of magnetic materials like iron, nickel, cobalt etc.

(ii) In a magnet, like poles repel each other, while unlike poles attract each other.

6. Where are poles of a bar magnet located?

Answer: The poles of the magnet are located at both the ends. When a magnet is placed on the iron material like iron filings, nails or pins spread on a paper, the iron materials stick onto the magnet. We can observe that most of the iron material stick onto the two ends of the bar magnet. These ends are called as the poles of the magnet.

7. A bar magnet has no markings to indicate its poles. How would you find out near which end is its north pole located?

Answer: A freely suspended bar magnet always comes to rest in the North−South direction. The north facing end of the magnet is its north pole, and the south facing end is its south pole.

8. You are given an iron strip. How will you make it into a magnet.

Answer: Place the given iron strip on the table. Take a bar magnet and place one of its poles near one edge of iron strip. Without lifting the bar magnet, move it along the length of the iron strip till you reach the other end. Now, lift the magnet and bring the pole to the same point of the iron strip from which you began. Move the magnet again along the iron strip in the same direction as done before. Repeat this process about 30-40 times. Bring a pin or some iron filings near the iron bar to check whether it has become a magnet. If not, continue the process for some more time to make the iron strip into a magnet.

9. How is a compass used to find directions?

Answer: A compass always points towards the North−South direction. The main arrow of the compass needle indicates its north pole. The arrow always points in the North direction. When we know of the directions, we can easily find all the other three directions. For example, If North is towards the front then South would be towards the back; East to the right of North and West to the left of North.

10. A magnet was brought from different directions towards a toy boat that has been floating in water in a tub.

Affect observed in each case is stated in Column I. Possible reasons for the observed affects are mentioned in Column II.

Match the statements given in Column I with those in Column II.

Column I Column II
Boat gets attracted towards the magnet Boat is fitted with a magnet with north pole towards its head
Boat is not affected by the magnet Boat is fitted with a magnet with south pole towards its head
Boat moves towards magnet if north pole of the magnet is brought near its head Boat has a small magnet fixed along its length
Boat moves away from the magnet when north pole is brought near its head Boat is made up of magnetic material
Boat floats without changing its direction Boat is made up of non-magnetic material

Answer: The following are the matched columns

Column I Column II
Boat gets attracted towards the magnet Boat is made up of magnetic material
Boat is not affected by the magnet Boat is made up of non-magnetic material
Boat moves towards magnet if north pole of the magnet is brought near its head Boat is fitted with a magnet with south pole towards its head
Boat moves away from the magnet when north pole is brought near its head Boat is fitted with a magnet with north pole towards its head
Boat floats without changing its direction Boat has a small magnet fixed along its length

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