Question:

A common transistor radio set requires $12 \mathrm{~V}$ (D.C.) for its operation. The D.C. source is constructed by using a transformer and a rectifier circuit, which are operated at $220 \mathrm{~V}$ (A.C.) on standard domestic A.C. supply. The number of turns of secondary coil are 24 , then the number of turns of primary are

Solution:

$\frac{N_{P}}{N_{S}}=\frac{V_{P}}{V_{S}}$

$\frac{N_{P}}{24}=\frac{220}{12}$

$N_{P}=\frac{220 \times 24}{12}$

$N_{P}=440$

Ans. 440 turns