QUESTION

# On what principle does an electric motor work?${\text{A}}{\text{.}}$ Electromagnetic induction${\text{B}}{\text{.}}$ When a rectangular coil is placed in a magnetic field and current is passing through it, a force acts on the coil which rotates it continuously.${\text{C}}{\text{.}}$ Both A and B${\text{D}}{\text{.}}$ None of the above

Hint: Here, we will proceed by telling what is done by an electric motor. Then, we will specify the working principle of an electric motor. Here, we will also state the process of electromagnetic induction.

An electric motor is a machine which converts electrical energy into mechanical energy.

It is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming's Left-hand rule and whose magnitude is given by
F = B$\times$I$\times$L where B is the magnetic field in weber per square meter, I is the current in amperes and L is the length of the coil in meters.

The force, current and the magnetic field are all in different directions.

Also given in option A, electromagnetic induction is a process in which a conductor is put in a particular position and the magnetic field keeps varying or the magnetic field is stationary and a conductor is moving. This produces a Voltage or EMF (Electromotive Force) across the electrical conductor.

Therefore, an electric motor works on the principle that when a rectangular coil is placed in a magnetic field and current is passing through it, a force acts on the coil which rotates it continuously.

Hence, option B is correct.

Note: An electric motor consists of armature coil, strong field magnet, split ring type commutator, brushes and battery. The split ring commutator helps in reversing the direction of the current in the armature coil. The brushes act as the contact between the commutator and the terminal battery.