Question

A 40 W lamp wastes 34 J of energy every second by heating its surroundings. What is the efficiency of the lamp?

Answer 1

Answer:

1.17

Explanation:

efficiency=

$\frac{power \: out}{power \: in} = \frac{40}{34} = 1.17$

Answer 2

Answer:

The efficiency of the lamp is 15%.

Explanation:

The efficiency is calculated as,

$\eta=\frac{U}{T} \times 100$     (1)

Where,

η=efficiency

U=useful energy per second that is given out

T= total energy per second

From the question we have,

T=40 Watt

U=40-34=6 Watt    (as the lamp wastes 34 J every second)

By placing the value of "U" and "T" in equation (1) we get;

$\eta=\frac{6}{40} \times 100$

$\eta=15\%$

Hence, the efficiency of the lamp is 15%.

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