Some students carry out investigations with an electric motor - Edexcel - GCSE Physics - Question 1 - 2012 - Paper 1

To calculate the input power (P) to the motor, we use the formula:

$P = V imes I$

where:

• V = voltage = 6 V
• I = current = 0.5 A

Thus, the input power is:

$P = 6 ext{ V} imes 0.5 ext{ A} = 3 ext{ W}$

The unit of power is Watts (W).

To find the wasted energy, we subtract the energy transferred to the weight from the input energy:

$\text{Wasted energy} = \text{Input energy} - \text{Energy transferred}$

$\text{Wasted energy} = 200 ext{ J} - 50 ext{ J} = 150 ext{ J}$

Efficiency (η) can be calculated using the formula:

$η = \frac{\text{Useful energy output}}{\text{Total energy input}} \times 100$

Substituting the known values:

$η = \frac{50 ext{ J}}{200 ext{ J}} \times 100 = 25\%$

Thus, the efficiency of the motor is 25%.