[3 Mark Question Answer]

Question 13 Marks

Define the following terms regarding a bar magnet,
a. Magnetic axis
b. Effective length
c. Magnetic equator
d. Magnetic field

Answer

a. An imaginary line (XY) passing through the magnetic north pole and magnetic south pole of a bar magnet is called its magnetic axis.
b. The distance (NS) between the north pole and south pole of a magnet is called the length or effective length of the magnet.
c. An imaginary line (PQ) bisecting the effective length of a magnet is called the magnetic equator of the magnet.
d. The region around a magnet where its magnetic force can be experienced is called the magnetic field.

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Question 23 Marks

What is a magnet ? Differentiate between natural and artificial magnets.

Answer

A magnet is a piece of metal that can attract metals such as iron, cobalt and nickel. Naturally occurring rocks such as Lodestone or magnetite have the ability of attracting magnetic substances and hence are called natural magnets. Magnets that are made by man from magnetic substances are called artificial magnets. These come in different shapes such as bar magnets, horse shoe magnets, disc magnets and ring magnets. Artificial magnets can be made in any size, shape or strength as desired but natural magnets cannot be made as desired.

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Question 33 Marks

How can a magnet be demagnetized ?

Answer

A magnet can be demagnetized in the following ways :

rough handling
hammering the magnet several times.
passing an alternating current around the magnet.
dropping the magnet on the floor several times.
heating the magnet to a very high temperature.

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Question 43 Marks

How can you make an electromagnet ? State the characteristics of an electromagnet.

Answer

Aim : To make an electromagnet.
Materials Required : An iron nail, a battery, a switch, some insulated copper wire and some iron paper pins.
Procedure : Coil the insulated copper wire around the iron nail. Connect the ends of the wire to the battery through the switch. Close the switch so that electric current flows through the copper wire. Now bring the iron paper pins close to the iron nail.
Observation And Conclusion : The paper pins get attracted to the nail, showing that the nail has turned into an electromagnet. Now, if you switch off the current, the iron paper pins will drop off the iron nail.

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Question 53 Marks

How is the single-touch method of magnetism different from the double-touch method ?

Answer

Single-touch method of magnetism:
1. A magnet is rubbed along the magnetic substance (needle or iron piece) from one end to another and lifted vertically upwards.

Double-touch method of magnetism :
1. Opposite poles of two magnets are placed next to each other at the centre of the magnetic substance and rubbed in opposite direction.

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Question 63 Marks

List four methods of magnetizing a magnetic substance.

Answer

Methods of magnetizing a magnetic material are :
1. Single-touch method – A magnet is rubbed along the magnetic substance from one end to another.
2. Double-touch method – Opposite poles of two magnets are placed next to each other at the centre of the magnetic substance and rubbed in opposite direction along it.
3. Magnetizing by induction – It is a method to make temporary magnets under the influence of a magnetizing force. The magnetic properties disappear when the influence of the magnetizing force is removed. (A permanent magnet is brought close to the magnetic substance but not touched.)
4. Electric current – A magnet made by using electric current is called an electromagnet. It is a temporary magnet and stops behaving like a magnet when the current is stopped. Electromagnets can become permanent magnets if certain
materials like steel and special alloys are placed in a coil and very strong current is passed through the coil.

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Question 73 Marks

Write a short note on the theory of magnetism.

Answer

All substances are made of minute particles. In a magnetic substance whether magnetized or non-magnetized), each individual particle behaves like an independent magnet. In the unmagnetized state, these particles within the substance are present in a random fashion such that they cancel out the magnetic effects of each other.

In a magnetized state, these particles align in a particle direction and the substance behaves like a magnet.

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Question 83 Marks

Distinguish between a temporary magnet and a permanent magnet.

Answer

Temporary magnet:

These magnets retain their magnetic property for a short duration of time.
These are made of soft iron.
They lose their magnetic properties once the magnetizing force is removed.

Permanent magnet:

These magnets retain their magnetic property always.
These are made of iron, steel, iron. cobalt, nickel or an alloy called ANILCO.
They retain their magnetic properties even after the magnetizing force is remov ed.

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