# Physics Questions and Answers – Bar Magnet

«
»

This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Bar Magnet”.

1. Which among the following is not attracted by magnets?
a) Iron
b) Cobalt
c) Copper
d) Nickel

Explanation: A magnet is a material that has both attractive and directive properties. It attracts small pieces of iron, nickel, cobalt, etc. This property of attraction is called magnetism. Going by this criteria, copper is not attracted by magnets.

2. Identify the direction in which a thin long piece of magnet comes to rest when suspended freely.
a) East-west
b) North-south
c) Northeast-southeast
d) Northwest-southwest

Explanation: When suspended freely, a thin long piece of magnet comes to rest nearly in the geographical north-south direction. When placed in a non-uniform magnetic field, it tends to move from weaker to stronger magnetic field.

3. Which of the following is not a basic property of magnets.
a) Magnet exists as a monopole
b) Attractive property
c) Directive property
d) Like poles repel and unlike poles attract

Explanation: Attractive property, directive property and the law of magnetic poles are some of the important properties of magnets. So unlike electric charges, magnetic monopoles do not exist. Every magnet exists as a dipole.

4. Give the SI unit of magnetic dipole moment.
a) A-2m
b) Am-2
c) A2m
d) Am2

Explanation: The magnetic dipole moment of a magnetic dipole is defined as the product of its pole strength and magnetic length. The SI unit of magnetic dipole moment is ampere metre2 (Am2). Magnetic dipole moment is a vector quantity and is directed from south to north pole of the magnet.

5. Which of the following is a natural magnet?
a) Magnetic needle
b) Bar magnet
c) Magnetite
d) Horseshoe magnet

Explanation: Pieces of naturally occurring iron ore, lodestone or magnetite had the property of attracting small pieces of iron. Hence, magnetite is a natural magnet. All natural magnets are permanent magnets, meaning they will never lose their magnetic power.

6. Magnetic lines of force always form open loops. State true or false.
a) True
b) False

Explanation: Magnetic poles always exist in pairs. So magnetic lines of force run from N-pole to S-pole outside the magnet and from S-pole to N-pole inside the magnet. They do not start or end anywhere and always forms closed loops.

7. A magnet can only repel another magnet. So, ‘X’ is a surer test of magnetism. Identify X.
a) Directive
b) Repulsion
c) Remanence
d) Hysteresis

Explanation: A magnet can attract another magnet or a magnetic substance like iron. However, a magnet can repel another magnet only. So repulsion is the surer test of magnetism.

8. A magnetic dipole of length 10 cm has pole strength of 20 Am. Find the magnetic moment of the dipole.
a) 2 Am2
b) 200 Am2
c) 20 Am2
d) 0.2 Am2

Explanation: Magnetic dipole moment = Pole strength × Magnetic length.
Magnetic dipole moment = 20 Am × 0.1 m
Magnetic dipole moment = 2 Am2.

9. A magnetized needle of the magnetic moment 20 JT-1 is placed at 60o with the direction of the uniform magnetic field of magnitude 9 T. What is the torque acting on the needle?
a) 225 J
b) 625 J
c) 155.8 J
d) 318 J

Explanation: Torque, τ = mBsin (θ).
Given: m = 20 J/T; B =9 T; θ = 60o
τ = 20 JT-1 × 9 T × sin(60o)
τ = 155.8J.

10. A bar magnet of the magnetic moment 5 Am2 has poles 20 cm apart. Calculate the pole strength.
a) 250 Am
b) 4 Am
c) 100 Am
d) 25 Am

Explanation: Magnetic dipole moment = Pole strength × Magnetic length.
Pole strength = $$\frac {Magnetic \, dipole \, moment}{Magnetic \, length}$$
Pole strength = $$\frac {5}{0.2}$$
Pole strength = 25 Am.

Sanfoundry Global Education & Learning Series – Physics – Class 12.

To practice all areas of Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.