Author: jmcminn

Year 6
Term 2

What have they taught us?
Light – How do the inventions of Percy Shaw work?
What is the relationship between light sources,
objects and shadows?

In this unit the children will:
Build upon the light work that they did in LKS2
Recognise that light appears to travel in straight lines
Use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye
Explain that we can see things because light travels from light sources to our eyes or from light sources to objects and then to our eyes
Use the idea that light travels in straight lines to explain why shadows have the same shape as the object that casts them
Plan different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary
Report and present findings from enquiries, including conclusions, casual relationships and explanations of and degree of trust in results, in oral and written forms such as displays and other presentations
Identify scientific evidence that has been used to support or refute ideas or arguments

Key Vocabulary
Shadow - a dark shape that is formed when an object blocks a source of light.
Reflection - When light from an object is reflected by a surface, it changes direction. It bounces off the surface at the same angle as it hits it.
Ultra violet (UV)- light of short wave lengths that humans cannot see but that can be seen by many animals
Ray - a model of light that is drawn as a straight line on diagrams
Beam - a directional projection of light energy radiating from a light source
Refraction - the changing in direction, or bending, of beam of light as it travels through a different transparent medium
Medium - the thing through which something is done eg light travels through the mediums of air and water etc..
Spectrum - We can only see light within a certain range of wavelengths and frequency. This range is called the visible spectrum.
Dispersion - the practice of separating a beam of white light into the individual colours that make up a beam of light.
dispersion

Key Knowledge
Percy Shaw
Percy Shaw was a British businessman and inventor. He is best known for inventing the cat’s eye, the reflective block that is set into roads to make it easier for motorists to identify the division between lanes and the edges of the roads at night.
Shaw was born in Yorkshire in 1890 and worked in a local mill when he was 13.
In the early 1920s, Shaw took his first ever holiday. He bought a bicycle, which at the time was a novelty, and cycled to London, a journey which took 3 days.
He came up with the idea for the cat’s eye when he was driving along a dark and winding road near his home. Shaw saw the eyes of a cat reflecting his headlights back to him.
In 1934, Shaw took a patent out on his device and created a company to manufacture it. The company was soon making over £1 million a year, partly due to the World War 2 blackout.
Percy Shaw even designed the cat’s eye to clean itself. When a car ran over the device, any rain water collected would wash over the glass surface, like human tears washing over a human eye.
How do we see?
We need light to see. Light comes from different light sources; our main natural light source is the sun. Other sources include fire, stars and man-made light sources such as light-bulbs and torches. The moon is not a source of light - it reflects the light from the sun
Our eyes see different wavelengths of light as different colours.
Light appears to travel in straight lines. We can see things because light travels from light sources to our eyes or from light sources to objects and then to our eyes. Light enters our eyes and hits the back of the eye (the retina). If the light is too intense it can damage the cells in the back of the eye.
Beams of light can be shown on a diagram as rays that travel from a light source to an object and then to our eyes. Arrows show the direction of travel of the light.

Shadows
Because light appears to travel in straight lines the shape of a shadow is defined by the shape of the object causing it. However, the size of the shadow can change; if you move the object towards the light source the shadow gets bigger. If you move the object away from the light source the shadow becomes smaller. In both cases the shape of the shadow remains the same.
Reflection of Light
When light from an object is reflected by a surface, it changes direction. It bounces off the surface at the same angle as it hits it. Smooth, shiny surfaces such as mirrors and polished metals reflect light well.
Because light appears to travel in straight lines mirrors can be used to see around corners and in devices such as telescopes, cameras and periscopes.
Refraction
When light travels from one medium to another its speed changes. Unless the light travels into the object at right angles to the surface there is also a change of direction. This is called
refraction and is why an object half in water appears to be bent and why when we view things underwater they are not where they appear be.
Dispersion
White light that comes from the sun and other sources, such as torch, is made up of a number of colours (red, orange, yellow, green, blue, indigo and violet) but we cannot see them because they are mixed together. The light can be split into the separate colours with a prism. This is called dispersion.