Question

The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a $220V$ A.C. supply. What will be the output voltage?

• A. $2volt$
• B. $2.2volt$
• C. $220volt$
• D. $22volt$

Answer 1

The correct option is B $2.2volt$

A transformer takes high-voltage electricity with a small current and changes it into low-voltage electricity with a large current, or vice versa. A step-up transformer turns low-voltage electricity into high-voltage electricity while dropping the current. A step-down transformer changes high-voltage electricity into low-voltage electricity.
If we change the number of turns in the coils we change the induced emf. This allows us to change (transform) the voltage from the primary to the secondary coil.
The Turns Rule is:

$\frac{Ns}{Np}=\frac{Vs}{Vp}$

Where,
Ns = number of turns on the secondary coil
Np = number of turns on the primary coil
Vs = voltage across the secondary coil
Vp = voltage across the primary coil
So if number of turns on the secondary coil(8 turns) is lesser than on the primary coil(800 turns), the output voltage will be lesser than the input voltage. This is called a step down transformer.
Hence, The output voltage as per the given question can be obtained as follows:
Let $x$ be the output voltage and the input voltage is given as $220V$.

$\frac{Ns}{Np}=\frac{Vs}{Vp}$;

That is,

$\frac{8}{800}=\frac{x}{220}$

$x=8\times \frac{220}{800}$ $=2.2V$

Therefore, the output voltage is 2.2V