Energy Transfers in Appliances Flashcards

All 6 cards in this deck

What does the power rating of a domestic appliance tell you?

The energy it transfers each second when in use, in joules per second (watts).

What are the steps to find the energy transferred by an appliance from its power rating?

e.g. a $1500\,\mathrm{W}$ heater used for $10\,\mathrm{s}$

1. Write $E = P \times t$
2. Substitute with time in seconds: $E = 1500 \times 10$
3. Energy transferred $= 15\,000\,\mathrm{J}$

Describe the energy transfer in an electric kettle connected to the a.c. mains.

Electrical energy from the mains is transferred to the thermal energy store of the heating element and water.

Describe the energy transfer in a battery-powered fan.

The chemical energy store of the battery is transferred electrically to the kinetic energy of the motor and fan blades (some is dissipated as thermal energy).

True or false? For the same time of use, a $2\,\mathrm{kW}$ heater transfers twice as much energy as a $1\,\mathrm{kW}$ heater.

True. $E = P \times t$, so energy is proportional to power rating for a fixed time.

True or false? A low power appliance can never transfer more energy than a high power one.

False. If it is used for long enough, a low power appliance can transfer more energy in total.