CAIE IGCSE Physics Efficiency Calculations

Practise calculating percentage efficiency from useful and total energy or power, then rearrange the ratio to determine an unknown input or output.

Exam points

calculate efficiency as useful energy output divided by total energy input × 100%
use useful power output divided by total power input when both quantities are rates
rearrange the efficiency ratio to find input energy, input power or useful output

[Maximum number: 2]

Fig. 3.1 shows a model of a wind turbine used to demonstrate the use of wind energy to generate electricity. The wind is blowing towards the model, as shown.

Fig. 3.1

The output current of the generator is 2.0 A . The output potential difference (p.d.) of the generator is 11 V .

Calculate the efficiency of the wind turbine.

(efficiency = ) $\mathrm{P}_{\mathrm{o}} / \mathrm{P}_{\mathrm{i}}$ OR (efficiency = ) $\mathrm{P}_{\mathrm{o}} / \mathrm{P}_{\mathrm{i}}$

OR (efficiency = ) $(11 \times 2 / 240) \times 100$

C1

\{efficiency $=(11 \times 2 / 240) \times 100=\} 9.2$ (\%)

A1

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1.7.3.7—Efficiency: (a) efficiency = useful question 1