Teaching about energy and energy transfer

Mike Evans and Linda Ellis

Introduction
Energy transfer
Energy forms
Key points
  Elements of the story

Introduction

Things change because of differences. Richard Boohan and Jon Ogborn argue that having energy does not make things change, rather that we need to think about the differences between things to explain change.

Differences might be in:

• concentration
• temperature
• pressure.

Energy transfer

A teaching model used by physicist Richard Feynman (see A model for the principle of energy transfer) involves thinking about energy as a series of units, like a child's bricks. Energy is transferred within and between systems, some ending up in one location while others end up in another. It is an easy step from this to Sankey diagrams.

In the classroom money or chocolate buttons are often used as the units of energy. These tokens represent the transfer of energy and can help to explain why a bulb in a circuit does not use up current. The current acts as an energy carrier. Indeed, money is a good analogy to use, since money itself is a token.

Along with this notion of energy there is a set of associated language. In this model of energy the energy is transferred from one place to another. Energy is located in particular positions. We speak of:

• energy being transferred from the battery to the bulb by electricity.
• energy being transferred from the bulb to the air (and to our eyes) by light.

The important aspect here is that energy is in a particular location and we do not talk about types of energy.

Energy forms

We will need to talk of energy being transformed from chemical energy in the battery to electrical energy in the wires, and to light energy in the bulb. We do not use the term 'transfer' here - it doesn't make sense.

If we adopt this view of energy, it is hard to develop adequate teaching models (visualisations) to explain what is happening in any change. This way of looking at energy can suggest that there is something magical going on as one form changes into another.

Throughout school science and beyond a mixture of these two approaches has been used, and not in consistent ways. Sometimes talking about electrical energy or light energy is helpful 'shorthand'.

However, there is a need to build on a firm base. How well do pupils and adults understand the concept of energy? How well are individuals able to use their view of energy to explain a range of everyday phenomena?

Key points

Energy conservation is the key concept that underpins our ability to track changes, account for what is happening and to make predictions. Twelve-year-olds can cope with this idea, but they do not readily understand it, since it is probably the most abstract idea we have in science.

Understanding comes through practice. Encouraging students to use the idea of energy transfer and conservation to track changes and to explain what is happening provides that practice. Why not, for instance, consider the energy transfers taking place using Sankey diagrams for photosynthesis and compare with a photovoltaic cell? Which is most efficient?

The elements towards building this story are given below. They are not necessarily in an order for teaching, since it is more efficient and effective to build the model as suggested by Feynmann. This roots the idea in a 'visualisation', or teaching model, which can then be used to track what is happening in a number of changes.

Elements of the story:

• Changes occur because of differences.
• These differences can be differences in terms of concentration, temperature or pressure (perhaps also momentum and potential?).
• When changes occur, energy is transferred from one location to another.
• During this process the total amount of energy is conserved.
• We can represent energy as a series of units (tokens or blocks etc.).
• We can measure energy in units called joules (J).
• As the result of a change, energy usually becomes less concentrated.
• We can represent these energy transfers as Sankey diagrams.
• When energy is concentrated in one place it is useful.
• Fuels are concentrated sources of energy.
• Energy can be stored and we usually refer to this as potential energy.
• Moving objects are a source of concentrated energy and we call this kinetic energy.
• An efficient system is one where a large percentage of the energy is transferred from one location to one other location.
• An inefficient system is where energy in one location is transferred to a number of different locations.
• This often happens when energy is transferred by heating.
• Systems in which energy is transferred from one place to one other are 100 per cent efficient. Is this achievable?

Because energy is an accounting system, the notion of energy transfer is best taught before energy sources. This then provides students with access to a wider range of models they can apply to help develop understanding, for example in electric circuits.