Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

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

30%

50%

90%

10%

Step-by-Step Solution

The efficiency ( $\eta$ ) of a transformer is defined as the ratio of output power ( $P_{out}$ ) to input power ( $P_{in}$ ).

Output Power: The lamp consumes 100 W. So, $P_{out} = 100$ W.
Input Power: The power drawn from the mains is given by the product of the primary voltage ( $V_p$ ) and the primary current ( $I_p$ ). $P_{in} = V_p I_p = 220 \text{ V} \times 0.5 \text{ A} = 110$ W .
Efficiency: $\eta = \frac{P_{out}}{P_{in}} \times 100\% = \frac{100}{110} \times 100\% \approx 90.9\%$ . The closest approximation among the options is 90%.

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