Explain the construction and working of the following. Draw a neat diagram and label it.

Electric Generator (AC)

#### Solution

**Electric Generator principle : **An electric generator is a machine that generates electricity by rotating its rotor in a magnetic field. Thus, it converts mechanical energy into electrical energy.

**Construction: **A generator consists of a rectangular coil MNST of insulated copper wire placed between two strong magnetic poles. The two ends of the coil MNST are connected with brushes A and B of rings C and D respectively. The inner sides of the rings are insulated. They are attached with an axle X*, *which can be rotated mechanically. Brushes A and B are connected with a galvanometer that can measure the flow of current in coil MNST.

**Working: **When the axle is rotated, lengths MN and ST move up and down respectively. Since lengths MN and ST are moving in a magnetic field, a current gets induced in these lengths caused by an electromagnetic induction. The direction of the induced current in both the lengths is given by **Fleming’s right hand rule**.

Since length MN is moving upwards in the magnetic field that acts from left to right, the direction of the induced current will be from M to N. Similarly, the direction of the induced current in length ST will be from S to T. Hence, an induced current will set up in the coil in the direction MNST, which produces deflection in the galvanometer.

After half-rotation, length MN starts moving down, whereas length ST starts moving up. The direction of the induced current in the coil gets reversed i.e., the induced current will now flow from T to M via S and N i.e., TSNM. Therefore, we can conclude that** after each half-rotation, the direction of the induced current is reversed**. This current is called an **alternating current (AC). An AC reverses its direction after equal time intervals**.