Question 14
HA student investigates the efficiency of a small electric motor.
The Figure shows the apparatus.
Figure
The motor lifts a mass of 0.20 kg through a height of 0.80 m. The reading on the joulemeter increases by 4.0 J.
Gravitational field strength = 10 N/kg
a.[3]
Calculate the efficiency of the motor.
b.
[2]
The student repeats the experiment with different masses.
The Table shows her results.
Table
| Mass lifted in kg\text{kg}kg | Efficiency |
|---|---|
| 0.10 | 0.25 |
| 0.20 | 0.40 |
| 0.30 | 0.48 |
| 0.40 | 0.44 |
| 0.50 | 0.35 |
Describe how the efficiency of the motor depends on the mass lifted.
c.[2]
Describe how the student could measure the height that the mass is lifted through as accurately as possible.
d.[1]
Suggest one way of increasing the efficiency of the motor.
7.2 Power and efficiency Questions
50 exam-style questions on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one has a worked solution and a mark scheme showing where the marks go.