Light, Sound and Waves

Light is travelling between source and effect

Teaching Guidance for 5-11 Supporting Physics Teaching

Light travels

Wrong Track: When a light is switched on the light fills the room and gets everywhere. The light is just there.

Right Lines: Light is travelling in straight lines, in all directions, in any illuminated space. The light fills the room to the extent that it is travelling through it.

Emphasising the point

Thinking about the learning

Some pupils entering high school are likely to have little idea of light being something that travels in the space between its source (for example, a torch) and the effect it produces (for example, a patch of light on the wall). They think of light as being a source or an effect.

Other pupils think of light as existing in space, but will say that it is just there. It does not move or do anything as such, but forms a pool of light around a light source.

Here light is considered to be like a pleasant aroma that fills a room. This point of view is reinforced by some of our everyday ways of talking: At that moment the entire hall was bathed in yellow light. Or the light from the security lamp filled the room when the intruder entered.

Thinking about the teaching

There is a significant job for the teacher in working with those pupils who think of light only in terms of a source and effect. The question of where light comes from in the first place will need to be posed and ideas of light travelling from source to effect introduced.

It is an interesting shift away from common sense to consider that your living room is light during the day because light is travelling through it in all directions and that it only looks light because light reflects off surfaces or any dust particles in the air and passes into your eye. At night when it is dark the only reason it is dark is that no light is travelling through the room. This is one of those cases where introducing a physics-based perspective necessarily involves making the familiar seem a bit odd.

is formalised by Law of Reflection
can be exhibited by Progressive Wave
has the special case Total Internal Reflection
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