A hairdryer contains a heating element and a fan driven by an electric motor.
On the hot setting, the input power of the hairdryer is 2.0 kW.
Describe the useful and wasted energy transfers in the heating element and in the motor when the hairdryer is on the hot setting.
The hairdryer is used on the hot setting for 12 minutes each day for 30 days.
Electricity costs 28p per kWh.
Calculate the cost of using the hairdryer for the 30 days.
A student says:
'The heating element is almost 100% efficient, but the motor is not.'
Explain why the student is correct.
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.