(a) What is an electric motor ? With the help of a labelled diagram, describe the working of a simple electric motor.
(b) What are the special features of commercial electric motors ?

Answer

### Step-by-Step Solution

#### (a) What is an electric motor? Describe the working of a simple electric motor with a labelled diagram.

1. **Definition of Electric Motor**:
An electric motor is a device that converts electrical energy into mechanical energy. It operates based on the interaction between magnetic fields and electric currents.

2. **Labelled Diagram**:
Draw a simple diagram of an electric motor. The diagram should include:
- A rectangular coil (ABCD)
- A power source (battery)
- Carbon brushes (P and Q)
- A commutator (half-ring)
- Magnetic field (indicated with arrows showing direction from North to South)

3. **Working of the Electric Motor**:
- **Current Flow**: When the motor is switched on, current flows from the battery through the carbon brush P into the coil ABCD.
- **Magnetic Field**: The magnetic field is established between the North and South poles.
- **Force on Coil**: According to Fleming's Left-Hand Rule, the forces acting on the sides of the coil are determined:
- The force on side AB is directed downward.
- The force on side CD is directed upward.
- **Rotation of Coil**: This creates a torque that causes the coil to rotate in an anticlockwise direction.
- **Commutation**: As the coil rotates and reaches the vertical position, the brushes touch the commutator, which reverses the direction of current in the coil. This reversal of current changes the direction of forces acting on the coil, allowing it to continue rotating.
- **Continuous Motion**: The process of current reversal occurs after every half rotation, enabling the coil to keep spinning as long as current flows through it.

#### (b) What are the special features of commercial electric motors?

1. **Soft Iron Core**:
Commercial electric motors are built on a soft iron core, which enhances the strength of the magnetic field, making the motor more powerful.

2. **Insulated Copper Wires**:
The coil in commercial motors consists of a large number of turns of insulated copper wire. This increases the efficiency and strength of the magnetic field.

3. **Powerful Electromagnets**:
Commercial motors often use powerful electromagnets as permanent magnets, which contribute to the overall efficiency and performance of the motor.