Energy is never used up. When a system changes, the energy only transfers between energy stores. Keep in mind, that a system just refers to an object or objects.
Four ways that energy can be transferred are:
You may see the terms mechanical work and electrical work. ‘Work’ is another way of saying energy is transferred.
During the heating process, energy can be transferred from a hot object to a cooler one by conduction, convection and radiation.
Conduction: Energy is transferred by direct contact.
Convection: Particles with more thermal energy take the place of particles with less thermal energy.
Radiation: Energy is transferred by electromagnetic radiation.
An example of this is when heating boiling water. The chemical energy store of the fuel decreases and the thermal energy store of the beaker and boiling water increases. Here, chemical energy is transferred to thermal energy.
Energy transfers and the locations of energy stores can be shown in an energy transfer diagram.
Let’s look at the energy transfer diagram of an electric lamp.
This diagram shows the transfer of energy with an electric lamp. The battery is a store of chemical energy, which is transferred to the lamp using wires, which then transfers to the surroundings as light.
The useful energy is the energy that is transferred as light energy (because we use lamps to lighten up a place). However, there are also some non-useful energy transfers, such as the energy that is transferred to the surroundings as thermal energy.
The total energy before and after a change or transfer remains the same, this is known as conservation of energy.
So: Total energy before = Total energy after