Question

A transformer steps up an AC supply from 220 V to 2200 V. If the secondary coil of the transformer has 2000 turns, the number of turns in its primary coil will be :

• A. 200
• B. 100
• C. 50
• D. 20

Answer 1

Answer: (A)

Answer is A.

A transformer takes high-voltage electricity with a small current and changes it into low-voltage electricity with a large current, or vice versa. That is, step up or step down the voltage in a circuit. 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:
Ns/Np=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 is more than on the primary coil, the output voltage will be higher than the input voltage. This is called a step up transformer.
Hence, The number of turns of the primary coil as per the given question can be obtained as follows:
Let input voltage be 220V and the output voltage be 2200V. Let 2000 be the number of turns of secondary coil and x be the number of turns of primary coil.
Ns/Np=Vs/Vp;
That is, 2000/x=2200/220
$x=\frac{2000\times 220}{2200}=200turns$.
Therefore, the number of turns of primary coil is 200 turns.