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WAEC Physics 2017 Paper

Question : 40

Total: 50

V_{r.m.s}

Solution:

Concept:

A transformer changes voltage based on the ratio of secondary to primary turns.

Explanation:

Given: primary voltage

E_p = 240\ \mathrm{V_{r.m.s}}

, primary turns

N_p = 3000

, secondary turns

N_s = 500

For an ideal transformer, the voltage ratio equals the turns ratio:

\frac{E_s}{E_p} = \frac{N_s}{N_p}

Substitute the known values:

\frac{E_s}{240} = \frac{500}{3000}

Simplify the ratio:

\frac{500}{3000} = \frac{1}{6}

Thus,

E_s = 240 \times \frac{1}{6} = 40\ \mathrm{V}

The output voltage is

40\ \mathrm{V_{r.m.s}}

Answer:

C. 40V

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