Question

Commercial electric motors do not use

• A. An electromagnet to rotate the armature
• B. Effectively large number of turns of conducting wire in the current-carrying coil
• C. A permanent magnet to rotate the armature
• D. A soft iron core on which the coil is wound

Answer 1

The correct option is C

A permanent magnet to rotate the armature

The explanation for correct option:

1. An electric motor is a mechanical device that converts electrical energy into mechanical energy.
2. Most electric motors work by connecting the motor's magnetic field and electric current in a wire winding to produce a force in the form of torque that acts on the motor's shaft.
3. A rectangular coil is situated between the magnetic field in an electric motor, and as current runs through the coil from the commutator rings, a torque operates on the coil, rotating it continually.
4. When the coil turns, the shaft connecting to it likewise rotates, resulting in mechanical work.
5. Field coils, not permanent magnets, are utilized in commercial electric motors to generate magnetic fields.
6. A strong magnetic field is created by whirling a large number of wire turns on a soft iron core.

The explanation for the incorrect option(s):

Option (A):

1. When current is fed through these coils, they become magnetic.
2. Field coils produce a more powerful, easily formed magnetic field than permanent magnets.

Option (B):

1. The magnetic field increases as the number of turns in the field coil increases.
2. As a result, the appropriate field coil sizes are used for a variety of commercial uses.

Option (D):

1. Commercial electric motors use a solenoid to rotate the armature.
2. The solenoid is also referred to as an electromagnet.

Therefore, the correct option is (C).