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Year 8 Light

revision for the Year 8 test

QuestionAnswer
What is the incident ray? The incoming ray.
What is the reflected ray? This is the outgoing ray.
What is the normal line? This is at right angles to the surface and from which angles are measured.
What is the angle of reflection? This is the angle between the normal and the reflected ray.
What is the angle of incidence? This is the angle between the normal and the incident ray.
Define refraction. This is the change in direction of light going from one material to another.
What is the meaning of 'absorption'? This is when energy is transferred from light to a material.
What is scattering of light? This is when light bounces off an object in all directions.
Define 'transparent' material. This is material that allows all light to pass through it.
What is translucent material. A material that allows some light to pass through it.
What is opaque material? Material that allows no light to pass through it.
Describe a convex lens. A lens that is thicker in the middle which bends light rays towards each other.
Describe a concave lens. A lens that is thinner in the middle which spreads out light rays.
What is the retina? The layer at the back of the eye with light detecting cells and where an image is formed.
How fast does light travel? Light travels at 300 million metres per second in a vacuum.
What happens when light enters a denser material, for example, a clear Perspex block. It bends towards the normal.
What happens when light enters a less dense material, for example, going from a clear Perspex block into air> It bends away from the normal.
What does the angle of incidence equal? The angle of reflection.
What does light travel in? Straight lines.
What happens when you shine light into a prism at an angle? It separates into the colours of a rainbow.
What is a luminous source? This is an object that can create light.
What is a non-luminous object. An object that does not create light.
How can we see non luminous objects? We see them because of the light reflected off of them.
What is bioluminescence? This is where organisms are able to create their own light.
What is reflection? When a wave hits a solid object it’s energy is reflected back the way it came. If this is light we see a reflection either of light or an image
What is specular reflection? This is the mirror-like reflection of waves, such as light, from a surface. Every ray of light is reflected at the same angle.
Explain diffuse reflection. With diffuse reflection, because the surface is not totally flat the rays of light bounce off in all directions so no clear picture can be formed.
What is the law of reflection? The angle of incidence is equal to the angle of reflection
In someone with clear vision, where does light focus? Exactly on the retina.
In a long sighted person, where does the light focus? Behind the retina.
In a short sighted person, where does the light focus? Before the retina.
How can short sight be corrected? With a concave lens.
How can long sight be corrected? With a convex lens.
What is white light made up of? Different colours.
What is the spectrum? The band of colours produced when light is spread out by a prism.
Why does a red object look red? Because it absorbs all the colours in the spectrum except red which it reflects.
Why does a black object look black? Because it absorbs all the colours in white light and doesn't reflect any.
What happens to a red object in green light? It looks black because it absorbs the green light but there is no red light to reflect.