Electromagnet

Q.

Boojho made an electromagnet by winding $50$turns of wire over an iron screw. Paheli also made an electromagnet by winding $100$ turns over a similar iron screw. Which electromagnet will attract more pins? Give reason.

Q.

The soft iron is used as the core of an electromagnet because

1. it can produce stronger magnetic field

2. it can easily get demagnetized

3. it is not expensive

4. it produces weak magnetic field

Q.

When the current is switched off, the electromagnet loses its magnetism.

1. True
2. False

Q.

Electromagnets are used in ___.

1. electric motor and generator

2. lifting and transporting heavy iron scraps

3. separating iron pieces from debris

4. magnetic compass.

Q.

Mention the applications of electromagnets.

Q.

Electromagnets are called permanent magnets.

1. True

2. False

Q.

Which of the following statements about an electromagnet is NOT true?

1. Electromagnets act as a magnet only when current passes through them.

2. Electromagnets are used in fans and radio.

3. Electromagnets are permanent magnets.

4. Electromagnets are made using insulated wires.

Q.

The strength of an electromagnet can be changed as per the needs.

1. True
2. False

Q. is used inside an electromagnet to make it stronger.

1. An alumium core
2. A soft steel core
3. A soft iron core
4. A hard iron core

Q.

The diagram shows a coil wound around a soft iron bar XY. The polarity at the ends X and Y are

1. X- north pole, Y- south pole

2. X- south pole, Y- north pole

3. X- north pole, Y- north pole

4. X-south pole, Y- south pole

Q.

Which of the following materials is the most suitable for making the core of an electromagnet?

1. Brass

2. Soft iron

3. Aluminium

4. Steel

Q.

Electromagnets are permanent magnets.

1. True

2. False

Q.

In which of the following cases the strength of the magnetic field inside an electromagnet would change?

1. If the number of coils in the electromagnet's winding is increased.

2. If the material of the core of electromagnet is changed.

3. If the current in the electromagnet winding is doubled.

4. If the direction of current in electromagnet winding is reversed.

Q. ntA straight magnetic wire of magnetic moment M is folded to form an arc that subtends an angle of 60^° at the centre of curvature .The new value of magnetic moment is A 2M/pi B 3M/pi C M/pi D M/3pin

Q.

The strength of an electromagnet can be increased by

1. increasing current in the coil

2. decreasing the number of turns of the coil

3. All of these

4. reversing the direction of current

Q.

Name two factors on which the strength of the magnetic field of an electromagnet depends.

Q.

Electromagnet is a,

1. Temporary magnet

2. Natural magnet

3. Permanent magnet

4. All of the above

Q. Which magnet allows the reversibility of its poles?

1. Bar magnet
2. Horseshoe magnet
3. Electromagnet
4. Disc magnet

Q.

Study the statements given below:
(i) Electromagnets can be made more powerful than ordinary bar magnets.
(ii) Soft iron is easy to magnetize and demagnetize.
(iii) The poles of an electromagnet are not affected by the direction of the current.

Which of the above statements about the electromagnets are correct?

1. Only (i) and (ii)

2. Only (ii) and (iii)

3. Only (i) and (iii)

4. (i), (ii) and (iii)

Q.

Find odd one out. Give reason for your choice.

1. bar magnet

2. horse-shoe magnet

3. electromagnet

4. lodestone magnet