Science lesson plan for Key Stage 2 – reflecting light and sound

This science lesson plan for Key Stage 2 works on a number of levels, writes Caroline Coxon

Light and sound comes into SC4, Physical Processes, and, in my experience, is studied as two separate units, with a number of lessons devoted to each. For most pupils, investigating light, how it travels, what stops it and which materials reflect it, is far more straightforward than learning about sound. To begin with, we can see light! We can see a torch beam as it travels across a darkened room and is bent when reflected from a mirror. We can’t see sound waves, even though, in many ways, they work in much the same manner as light waves. This is why I decided to tackle them in parallel – not to confuse, but to improve the understanding of one with study of the other. This seemed to provide a perfect opportunity for G&T pupils to take on the more complex investigations of sound waves and how they are reflected (or not) by different materials, at the same time as other pupils carry out a very similar investigation with light.

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The pupils can be grouped simply by task – ‘the light group’ and ‘the sound group,’ so that no one stands out as being ‘better’ than others. The G&T pupils will find their sound work just as demanding as their peers will find the light work. In order to challenge the G&T group’s problem-solving skills, provide them with some equipment and expect them to devise their own investigation, with results table. (However, as a failsafe, have the instructions in a sealed envelope, which they are to open if they haven’t come up with something appropriate in 10 minutes or so.)

Results

There will be some cross-over in the results from the two sets of investigations. For example, with both light and sound, the mirror will almost certainly prove to be the most effective as a medium for reflection. I would expect the G&T students to be able to work out why this is – what qualities in the material are important for each and why it is that, for example, plastic reflects sound well, but not light.

Plenary

The plenary is an important platform for the G&T pupils to demonstrate their understanding. The other pupils will talk about their ‘light’ investigations, the outcomes of which are likely to have been already grasped by G&T pupils. Then the G&T pupils will talk about their ‘sound’ studies, which should be effective in allowing others to be able to make the link, and therefore better understand the properties of sound. Discussion can revolve around everyday applications for their findings, eg: In pairs/groups list circumstances when we want good light/sound reflection. When and where might we want to limit light/sound reflection? (Home, school, place of work, hospital, theatre, library.)

The two experiments Light: In a dim or darkened room, the pupils shine a torch at a set angle on to a variety of materials so that the beam is reflected on to a wall (or not, if the material is non-reflective). The reflection can be assessed on a scale of 1-4 so a graph could be drawn to display the results.

Very clear to see (very good reflection = 4) Quite clear to see Difficult to see Very difficult to see/cannot be seen (very poor reflection = 1) If the beam of the torch is too diffuse, then duct tape stuck over the glass front of the torch could be used to narrow it, or make a shape that could be reflected on to the wall (a cross for example).

Sound:

On a table-top one of the materials is held upright. Two cardboard tubes are angled in a V-shape, the point about 6cms from the material. The tubes should be reasonably long (50cm or longer) and the diameter of the tube should be sufficiently large so that an ear can be pressed to it. The ticking clock/timer is placed at the entrance to one tube, and a member of the group listens at the entrance to the other tube. Part of the G&T problem solving will be how to separate sound and reflected sound eg by covering the ear not pressed to the tube, or using some sort of sound barrier. G&T pupils can devise their own four-point scale for recording the clarity of sound reflected and therefore the effectiveness of different materials as ‘reflectors’.

The extension activities

Echoes:

Some necessary facts: sound travels at about 33m in 0.1 seconds, so it is only possible to hear an echo if the wall that the sound bounces off is at least 17m away. Although pupils will not know the figures, they might be able to work out why it is that echoes aren’t heard in small rooms.

Sonar game:

The pupils could think along the lines of ‘Squeak, piggy, squeak’ where the blind-folded ‘bat’ has to locate the position of the ‘insect’ (not the identity of the insect). The bat has to squeak, and the insect has to squeak in response, until the insect is ‘captured.’