Draw and interpret diagrams to represent energy transfers

The idea

An energy transfer diagram shows a store or pathway on the left, an arrow for the transfer, and the stores that gain energy on the right. Draw boxes for stores such as chemical, kinetic, gravitational potential and thermal, and label arrows with the pathway: heating, radiation (including light), electrical work or mechanical work. For a torch, draw a chemical store box, an arrow labelled 'electrical work' to a thermal store box, and a second arrow labelled 'radiation' to the surroundings; light is a radiation pathway, never a store. Interpret a given diagram by naming the starting store, the pathway and the final store, and by stating whether energy is conserved.

What earns the marks

• Names the starting energy store and the final energy store shown in the diagram.
• Labels each arrow with a transfer pathway such as heating, radiation, electrical work or mechanical work.
• Identifies light as a radiation pathway rather than an energy store.
• States that the total energy is conserved because the energy transferred out of one store equals the energy transferred into others.

Common mistakes and how to put them right

• Labels light as an energy store.

  Put it right: Label it as a radiation pathway instead.

• Writes an arrow with no pathway label.

  Put it right: Add the pathway such as heating or electrical work.

• Omits the surroundings as a final store when energy is dissipated.

  Put it right: Include a thermal store for the surroundings.

Exam tips

• Draw boxes for stores and arrows for pathways, and keep the two clearly different.
• Read the question's command word: 'draw' needs a labelled diagram, 'interpret' needs named stores and pathways in words.
• Check that every arrow carries a pathway label before you finish.