Question

The primary coil of a transformer is connected to an AC source of voltage $60V$. The turn ratio of the transformer is $3:1$. What is the secondary or output voltage of the transformer?
(A) $18V$
(B) $20V$
(C) $2V$
(D) $180V$

Answer 1

Hint Transformer is used to change voltage of AC electricity. Voltage of electricity is changed with respect to the turn ratio of the transformer. If turns in primary coil are more than turns in secondary coil the voltage decreased by a factor which is equal to ratio of turns of transformer and vice versa. Or ratio of voltages of coil is equal to turn ratio of transformer.

Complete step by step solution
Primary voltage is $60V$ and the turn ratio of the transformer is $3:1$ as given.
Let $N_1$ be the number of primary turns and $N_2$ be the number of secondary turns. And $E_1$ and $E_2$ are primary and secondary voltages of the transformer.
Given, $E_1=60V$ and ${\displaystyle \frac{N_1}{N_2}}=3$.
We know that,
${\displaystyle \frac{E_1}{E_2}}={\displaystyle \frac{N_1}{N_2}}$ or $E_2=E_1\times {\displaystyle \frac{N_2}{N_1}}$
Then, $$E_2={\displaystyle \frac{60}{3}}=20V$$.

Hence, correct answer is option B.

Note There are two types of transformers: step-up and step down. Here the given transformer is a step-down transformer as primary voltage is more than secondary voltage. Current in circuit also balance in transformer, for ideal transformer product of voltage and current in primary coil is equal to product of voltage and current in secondary voltage. If voltage is increased by the transformer then current is decreased in the circuit.