Energy Transfers: Answers

What is meant by the term ‘conservation of energy’?

The ‘conservation of energy’ means that the total amount of energy in a system always remains the same (i.e. it is conserved. It cannot be created or destroyed, but it can be converted from one form of energy into another.

What are the 8 different types of energy store?

The eight different types of energy are: nuclear, chemical, magnetic, gravitational potential, kinetic, thermal, elastic potential and electrostatic. You can use the mnemonic ‘Naomi Campbell Met Grace Kelly To Eat Enchiladads’ to help you to remember.

How can energy be converted from one form into another?

Energy can be converted from one form to another in the following ways: mechanically, electrically, by heating or by radiation.

Calculate the efficiency of a lamp which converts 600 J of electrical energy into 65 J of light energy and 535 J of heat energy.

In a lamp, the useful form of energy is light energy. Any other forms of energy are wasted energy. The efficiency of the lamp is therefore (65/600) x 100 = 10.8%.

The equation to work out efficiency is: (useful energy / total energy) x 100

Describe the three ways in which thermal energy moves in the environment.

Thermal energy moves by conduction, convection and radiation. Conduction happens when heat is transferred through solid materials which are physically touching (e.g. frying an egg on a metal pan). Convection happens in fluids (liquids and gases) when warmer parts rise due to their lower density. Cold parts move to take up the space, generating convection currents. This happens when we turn on the radiator in our homes. As the air close to the radiator heats up, it rises and is replaced by cooler air which is then heated by the radiator. Radiation happens when objects emits infrared radiation (heat). All objects do this, including you. This is why a room full of people feels much warmer compared to an empty one.

Give examples of the way in which the loss of thermal energy from a house can be reduced.

Heat loss from a house can be reduced using cavity wall insulation (to reduce conduction), draught excluders and double glazing (to reduce convection) and by painting the house light colours (to reduce radiation).