# What are AC Generators and Transformers?

Did you know that when electrostatic generators were first used there was no relationship between the electricity and magnetism? Those generators were inefficient and were never used further. A generator simply converts mechanical energy into electrical energy. AC generator is based on the principle of Faraday’s law of electromagnetic induction.

It consists of a rectangular coil with a number of copper wires wounded over an iron core. The coil is called the armature. It is used to increase the magnetic flux. A strong permanent magnet is placed and the armature is rotated between the magnets where the magnetic lines are perpendicular to the axis of the armature. There are two slip rings connected to the arms of the armature. They are used to provide movable contact. Two metallic brushes are connected to the slip rings to pass current from the armature to the slip rings. The current is passed through a load resistance which is connected across the slip rings.

At different time intervals, the position of the armature keeps changing. When the magnetic field lines are perpendicular to the coil, the coil is rotated in the magnetic field and the induced e.m.f produced increases. This happens in this position because of the number of intercepting magnetic field lines maximum.

## What is a Transformer?

You must have heard about transformers, do you know what is the main purpose of a transformer?
Transformers are used for the transmission of electrical energy. A transformer works on the principle of mutual induction. At a different voltage level, transformers can change the electrical energy of a given voltage.

It consists of two coils named as Primary coil and a Secondary coil which is wound on a soft iron core. The soft iron core is laminated to minimize eddy currents. The alternating current is applied across the primary coil and the output is obtained across the secondary coil.

## Types of Transformers

There are two types of transformers:

• Step-up Transformer
• Step-down Transformer

Step-up Transformer converts a low voltage into a high voltage. The number of turns in the primary coil is less than the number of turns in the secondary coil, i.e. $$N_p~<~N_s$$. Step-down Transformer converts a high voltage when current decreases into a low voltage when current increases. The number of turns in the primary coil is greater than the number of turns in the secondary coil, i.e. $$N_p~>~ N_s$$.

According to Faraday’s law of electromagnetic induction, the induced e.m.f is given by:

$$e$$ = $$-\frac{dϕ}{dt}$$
$$e_p$$ = $$-\frac{dϕ_p}{dt}$$
$$e_s$$ = $$-\frac{dϕ_s}{dt}$$

By using the above equations, we get,

$$e_s$$ = $${N_s}{N_p}~e_p$$

The ratio $${N_s}{N_p}$$ = $$k$$, it is called transformation ratio. Know more about Generators and Transformers by downloading BYJU’S – The Learning App.

#### Practise This Question

The number of turns in the coil of an ac­ generator is 5000 and the area of the coil is
0.25m2. The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2 W/m2. The peak value of the emf generated is nearly