JEE Main 2025 Apr 3 Shift 2, Physics Q18: Energy, Power And Heating Effect

JEE Main2025Apr 3, Shift 2Physics

A motor operating on $100$ V draws a current of $1$ A. If the efficiency of the motor is $91.6%$ , then the loss of power in units of cal/s is

Solution

Input power: $P_{in} = V I = 100 \cdot 1 = 100$ W.

Useful output: $P_{o u t} = 0.916 \cdot 100 = 91.6$ W.

Loss: $P_{l oss} = 100 - 91.6 = 8.4$ W $= 8.4$ J/s.

Convert to cal/s using $1$ cal $= 4.2$ J:

$P_{l oss} = \frac{8.4}{4.2} = 2$ cal/s.

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