Energy Transfers and Work Done

Energy Transfers

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:

  • Mechanically – The action of a force to move an object across a distance
  • Electrically – By an electrical current
  • By radiation – Electromagnetic waves
  • By heating – Conduction, convection and radiation

You may see the terms mechanical work and electrical work. ‘Work’ is another way of saying energy is transferred.

Energy transfer by heating

During the heating process, energy can be transferred from a hot object to a cooler one by conductionconvection and radiation.

A pot with the lower half of the liquid it contains coloured red and the top half blue. Arrows going up and down represent convection, orange arrows emitted from the heat source represent radiation and the hot handles of the pot labelled conduction.

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 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.

A beaker above a bunsen burner with water vapour rising out of the beaker.

Energy Transfer Diagram

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.

Battery to a lamp with some heat transferred to the surroundings and light energy transferred to the surroundings. The heat is labelled as not useful.

This diagram shows the transfer of energy in 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 transferred as light (because we use lamps to light 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.

A cracked dim light bulb.

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

You’ve used 5 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up