Light can travel through certain materials, such as glass, water, clear plastic and such materials are called transparent.
Coloured filters allow light through but we shall consider these in more detail when we think about colour.
Translucent materials, like greaseproof paper and frosted glass let some but not all light through. They scatter or diffuse the light.
Opaque materials and shadows
Most materials do not allow light through at all and these are called opaque. When light from a source cannot travel through a material then a shadow can be formed. This is shown in the following diagrams where the path of the light is shown by a straight line with an arrow. The rays shown are sample rays from the edges of the girl causing the shadow. The formation or shadows in this way shows that light travels in straight lines.
A shadow is actually the absence of light.The size of the shadow in the diagrams depends on the distance of the girl from the torch. The drawing of the rays of light, or ray diagrams as they are known, shows that the closer the girl to the light source, the larger the shadow.
Ideas for primary activities:
ContentsSight, Safety, Light needs a source, Speed of Light