Rankers Physics

Alternating Current: Practice Problem & Solution

46. 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 amp, the efficiency of the transformer is approximately: (2007)
50%
90%
10%
30%

Solution Explained:

To solve this problem, we apply the core principles of Alternating Current. Understanding the underlying formula is key to arriving at the correct answer below:

Output power is $P_{out} = 100 W$.
Input power is $P_{in} = V_p I_p = 220 \times 0.5 = 110 W$.
Efficiency $\eta = \frac{P_{out}}{P_{in}} = \frac{100}{110} = 0.909$, which is approximately $90\%$.

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