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 crate the armature
D. A soft iron core on which the coil is wound

Answer 1

Recall the working of commercial motors. Also remember the components that are required for its working. Cross check those components with those given in the options and see which among these doesn’t form a part of an electric motor. Also, give a short justification as to why it isn’t used.

Complete answer:
We know that an electric motor is an electrical machine that converts electrical energy into mechanical energy. They operate as the result of interaction between the motor’s magnetic field and electric current in a wire winding which further generates a force in the form of torque applied on the motor's shaft. Direct current (DC) sources as well as alternating current (AC) sources both can power electric motors.

The basic components of an electric motor are:
(a) A power source that supplies power to motor armature or field coils.
(b) A commutator which is a rotating interface of the armature coil with a stationary circuit.
(c) An armature coil that aids the motor to run.
(d) An armature core that holds the armature in the plane and also provides mechanical support.
(e) A field magnet that is responsible for the production of torque on the rotating armature coil.
(f) The brushes that conduct current between stationary wires and moving parts.
So we see that a commercial motor uses an electromagnet, a large number of turns in the current carrying coil, a soft iron core on which the coil is wound, also an armature which is a combination of soft iron core and coil. But the electric motors do not use permanent magnets to rotate armature as they are weak magnets and an electric motor definitely requires a magnet (permanent magnet) that produces a strong magnetic field for its working.

Note:
Electric motors have a lot of applications. They are used in drills, water pumps, hard disk drives, washing machines and industrial equipment. Generators function just opposite to how motors work. Generators convert mechanical work to electrical energy. Also the more the number of turns in the field coils is the more the magnetic field will be.