Can light bend? REFRACTION
Have you ever wondered Disappearing Coin Trick Can you explain what happens?
Refraction Starter: Why does the pencil appear bent in the water?
The pencil appears bent because light travels at different speeds in different materials. This causes the light to bend/refract. Refraction is the change in the direction of light.
Objectives: Describe what happens to light when it passes through materials of different densities Draw ray diagrams to show refraction of light Key word Refraction Refraction the bending of light when it passes through a different medium
Imagine you re running along this beach and then into the water. Would you be moving slower in the water or on the beach? The speed of light also changes from one medium to anotheras the density changes. How do you think the speed of light changes with density?
Refraction at an air-glass boundary
Investigating Refraction An investigation to find out what happens when light travels through a glass block Draw table... Angle of Incidence ( ) 0 30 42 60 90 Angle of Refraction ( )
Refraction in a glass block
Investigation Angle i 1) Draw around a rectangular block Angle r 2) Draw a normal line 90º from the top of the block 3) Shine light into the block, making sure it hits it where the normal line crosses the glass surface. 4) Draw the rays of light entering and leaving your block onto your paper 5) Remove the block and draw cgrahamphysics.com a line 2016 across the block
Investigation Questions: 1) What happens to the ray as it enters the glass? 2) What happens to the ray as it re-enters the air?
Air to Glass: angle of incidence > angle of refraction i > r i > r If light rays move from a less dense medium (air) to a more dense medium (glass) they move towards the normal.
Glass to Air: angle of incidence < angle of refraction i < r If light rays move from a more dense medium (glass) to a less dense medium (air) they move away from the normal. i < r
Refraction ray diagram
Effects of refraction the Archer fish The archer fish is a predator that shoots jets of water at insects near the surface of the water. The archer fish allows for the refraction of light at the surface of the water when aiming at its prey. image of prey The fish does not aim at the refracted image it sees but at a location where it knows the prey to be. prey location
Why is light refracted? The speed of light depends on the material through which the light is travelling. When light enters a different material (e.g. when moving from air into glass), the speed of light changes. This causes the light to bend or refract. air glass The speed of light is affected by the density of the material through which it is travelling. When light enters a more dense medium, its speed decreases and this is why refraction occurs.
Effects of refraction Light from the part of the pencil in the water is refracted as it travels from the water into the air, making it appear bent. How does refraction make this stone look closer to the surface of the water than it really is? Light rays from the stone are refracted as they leave the water. The brain assumes the rays have travelled in straight lines, and is fooled into forming an image where it thinks the light rays came from.
When light bends this refraction is called ---------- Refraction ---------- happens because the light changes speed. When light enters a more ---- dense medium [e.g. glass], it bends towards ------ the normal. When light enters a less ---- dense medium [e.g. air], it bends away --------the from normal.
Uses of Refraction? Lenses: Your eye Magnifying glass Spectacles Cameras Telescopes Microscopes
Refraction true or false?
Plenary: Answer A, B, C or D 1) Refraction is what happens when light: A hits an opaque object B bounces off a mirror C is scattered unevenly by a rough surface D changes direction as it goes from one substance into another
Plenary: Answer A, B, C or D 2) Refraction occurs because: A light speeds up when it goes from air to glass or water B light slows down when it goes from air to glass or water C light stops when it goes from air to glass or water D light reflects inside transparent cgrahamphysics.com materials 2016
Plenary: Answer A, B, C or D 3) Why does a lens change the path of light? A Light changes direction when it goes into the glass and when it comes out of it B Light changes direction in the centre of the lens C Light is reflected by the surface of the lens D Light travels faster in glass than it does in air