Chapter 14: Energy Transfers
1 State the seven energy stores.
2 For each of the following situations, write down the energy input, energy transfer and energy
output.
a a bungee jump
b an oscillating spring
c a burning candle d a
TV set
e a nuclear power station
3 a State the principle of conservation of energy.
b A filament light bulb is supplied with 100 J of energy. It transfers 10 J as light energy. Calculate
the percentage efficiency of the light bulb.
c A new energy efficient light bulb is produced. It has an efficiency of 0.66. Calculate the useful
energy transferred if the new bulb is supplied with 40 J of energy.
© Pearson Education Ltd 2018. Copying permitted for purchasing institution only. This material is not copyright free.
4 a A hairdryer transfers 2000 J of electrical energy as 1500 J of useful kinetic and thermal energy
from the motor and 500 J of wasted sound and heat energy in the components. Draw a
Sankey diagram to illustrate this energy transfer.
b Calculate the efficiency of the hairdryer.
5 A toaster is 50% efficient. 750 J of energy provided to the toaster is transferred to the bread as
heat energy, 450 J is transferred to the surroundings as heat and 300 J is transferred as light and
sound.
a Calculate the total energy supplied to the toaster.
© Pearson Education Ltd 2018. Copying permitted for purchasing institution only. This material is not copyright free.
b Use the information from part a to draw a Sankey diagram to represent the energy transfers.
© Pearson Education Ltd 2018. Copying permitted for purchasing institution only. This material is not copyright free.