Question

In which of the following devices is a permanent magnet not used?

• A. Electric motor
• B. Telegraph
• C. Generators
• D. Particle accelerators

Answer 1

The correct option is B

Telegraph

Explanation

1. Permanent magnets are those magnets that are commonly used. They are known as permanent magnets because they do not lose their magnetic property once they are magnetized.
2. Temporary magnets can be magnetized in the presence of a magnetic field. When the magnetic field is removed, these materials lose their magnetic property.

The explanation for the correct option:
Option B:

1. Telegraph is a device in which a permanent magnet is not used.
2. An electromagnet is used in the telegraph.

The explanation for the incorrect option(s):

1. Permanent magnets are used in dynamos and electric motors.
2. It is also used in generators, electron accelerators, door locks, etc.
3. Thus options A, C, and D are not correct.

Therefore, the correct option is option B