Science at key stage 3    (Year 8)

• Review pupils' understanding of light by asking them Where is there light in this room? Help them to develop the idea of light travelling and to recognise that although, when a light is switched on, its effects on objects seem instantaneous, this is because light travels at immense speed. Recall their experience of thunder and lightning, to show that light travels much faster than sound.
• Ask pupils for suggestions on how we could show that light moves, eg how a lighthouse works. Help pupils to carry out a thought experiment. Ask them to imagine what would happen if the source were moved further and further away from an object, and help them to understand that, at great distances, there is a lapse of time between leaving one and meeting the other. Some will have heard of the speed of light. Help them towards an understanding of this very large number by relating it to everyday speeds and distances, and comparing these with the distance between stars.

• Carry out a range of quick activities designed to develop the idea that light travels in straight lines, eg producing a shadow from a strong source, trying to look down a piece of rubber tubing, showing images of light rays shining through clouds, light rays in a mist, spotlight beams, light beams being reflected in a mirror. Encourage pupils to try to explain these phenomena in terms of a sequence beginning with light leaving the source and finally hitting a screen. Help pupils to use the idea of light travelling in straight lines in their explanation.
• Demonstrate how we can test the idea by shining a beam of light through a series of holes in pieces of card arranged one behind the other. Reinforce this concept by showing a laser beam and sprinkling talc or chalk dust in its path.
• Introduce the use of rays to represent light and ask pupils to draw diagrams of the evidence they have seen, using such lines to show the path taken by light in each case.

• Provide a range of materials for pupils to sort into transparent, translucent or opaque groups, by shining light from a ray box onto them. Ask them to explain what is happening to the light in each case, and introduce the ideas of reflection, transmission and absorption.
• Extend this work by allowing pupils to use a light sensor with a datalogger to compare the amount of light that is reflected by or transmitted through the different materials.
• Establish that materials reflect or transmit different amounts of light and ask pupils to suggest what has happened to the rest of the light, developing the idea of absorption.

• Elicit pupils' ideas about how we see things. Use their views to develop the idea that light travels into our eyes from luminous objects for us to see things. Extend this to non-luminous objects.
• Provide pupils with a picture containing luminous and non-luminous objects, and ask them to draw in some of the light rays that enable us to see these objects.

• Introduce reflection using a torch in a darkened room. Ask pupils to predict where reflected rays will go.
• Demonstrate the use of a ray box and slit to produce a thin beam of light. Ask pupils to predict what will happen if the beam shines onto a plane mirror, to record their prediction, and to plan how to investigate their predictions of reflections at such a surface. Point out the need for accurate measurement and show them how to measure angles of light rays with reference to the normal, using a protractor, and to draw a line graph of their results. Through questioning, establish whether the data collected supports the pupils' predictions.
• Ask pupils to find out how infrared remote-control devices work and whether infrared is reflected in a similar way to light.

• Introduce the idea of the nature of a 'mirror image' produced in a plane mirror. Ask pupils how such an image differs from the object viewed, and explore their explanations of why this happens, eg pupils could, in pairs, model object and image in a mirror.
• Ask pupils to explore the symmetry of images by predicting and testing which capital letters or words are symmetrical and by predicting the number of images formed of an object placed between two plane mirrors set at different angles. Encourage pattern seeking so that pupils can make predictions. Show how to 'see yourself as others see you' in two mirrors set at 90° to each other.

• Present pupils with a range of examples of how reflections are used and ask for explanations of how they work, eg reflective cycle clothing, reversed ambulance signs, kaleidoscope, periscope, Pepper's ghost.

• Demonstrate simple situations involving refraction, eg pencil in beaker of water appears to bend, and the strange views perceived when looking through water, eg in a swimming pool. Introduce the idea of light changing direction when it passes from one transparent medium to another, and the term 'refraction', and distinguish this from reflection. Help pupils to interpret what they see by explaining that they imagine light as having travelled in a straight line rather than as having been refracted (bent).
• Provide a range of glass or perspex blocks of different shapes, including rectangular and semicircular, and ask pupils to investigate their effects on a single ray of light produced by a ray box. Ask them to look for patterns in their observations of reflection when changing the angle of incidence. Establish generalisations from patterns of observations.
• Set up the 'disappearing coin in a cup of water' demonstration. Ask pupils to explain how it works.

• Demonstrate how white light can produce a spectrum when shone through a prism, and describe the work of Isaac Newton in this field. Ask questions about colours, eg Can you really see seven colours?
• Provide pupils with prisms and ask them to explore and record the images they see in them.
• Allow pupils to make their own spectrum and challenge them to suggest how the coloured rays could be remixed. Help them to achieve this, using a second prism, and develop the idea that white light consists of a mixture of different coloured lights, which can be separated and combined.

• Ask pupils to explore how coloured filters affect light, eg by producing a spectrum and allowing this to pass through filters of different colours; by passing white light through one filter and then through a second filter.
• Remind pupils of their earlier work on absorption and transmission of light, and on the nature of coloured light as demonstrated by the spectrum. Ask pupils to explain why light appears to change colour as it passes through.
• Establish the idea that coloured filters will only transmit light of certain colours, the other colours being absorbed, and help pupils illustrate this with annotated diagrams.
• Demonstrate, using an overhead projector (OHP), software or video clips, how the primary colours of light can be combined to produce white light, and briefly discuss the relevance of colour vision and the production of coloured pictures on television.

• Ask pupils to investigate the effects of viewing different coloured objects in beams of light of different colours. They should collect a range of observations as a table, and try to find patterns in these. Ask pupils about applications of this effect, eg in disco lighting, in matching dyes in fabrics, in identifying colour of clothing under street lighting.

• Provide pictures of a series of mirrors, opaque materials and transparent blocks and ask pupils to complete the paths of a light ray incident on them.
• Ask pupils to design the lighting for a theatre production in which particular colour effects are desired, and to present their suggestions to the group or whole class.
• Ask pupils to describe and explain any optical effect that has particularly impressed them, eg laser display.