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Electromagnetic Induction

Question

A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately

30%

50%

90%

10%

Solution

90%

The efficiency of the transformer

$= \frac{Energy obtained from the secoindary coil}{Energy given to the primary coil}$

$η = \frac{Output power}{Input power} \Rightarrow η = \frac{V_{s} I_{s}}{V_{p} I_{p}}$

Given:- V_s I_s = 100 W,

V_p = 220 V,

I_p = 0.5 A

$η = \frac{100}{220 \times 0.5} = 0.90 η = 90 %$