A common transistor radio set requires 12 V (D.C.) for its operation. The D.C.
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:

$(440)$

Given

Primary voltage, $V_{p}=220 \mathrm{~V}$

Secondary voltage, $v_{s}=12 \mathrm{~V}$

No. of turns in secondary coil is $\mathrm{N}_{\mathrm{s}}=24$

no. of turns in primary coil, $\mathrm{N}_{\mathrm{p}}=$ ?

We know that for a transformer

$\Rightarrow \frac{N_{p}}{N_{s}}=\frac{V_{p}}{V_{s}}$

$\Rightarrow N_{p}=\frac{V_{p} \times N_{s}}{V_{s}}=\frac{220 \times 24}{12}$

$\Rightarrow N_{p}=440$