Refraction Date Key words Reflection Reflected Ray Incident Ray Normal Refraction Convex What do you think is happening in the above photo and why? https://www.youtube.com/watch?v=o08jgkut7e8
Refraction Learning Objectives Investigate the behaviour of light as it travels from one medium to another. Explain the process of refraction using key scientific terms. Construct ray diagrams.
Refraction investigation 13 of 20 84 1. Place a rectangular glass block on a sheet of paper and draw around it. 2. Draw a normal line (at 90º) along the top surface of the block. angle i angle r 3. Shine rays of light with incident [i] angles of 0º, 20º, 40º, 60º, 80º and 90º into the block, making sure they all hit where the normal line crosses the glass surface. Measure angle r each time and record the results.
Refraction investigation results Record the results of the refraction investigation in a table: Angle of incidence [i] 20º Angle of refraction [r] 40º 60º 80º 90º Describe the change of direction of: the ray as it enters the glass; the ray as it re-enters the air. 14 of 20 84
Refraction in a rectangular block 15 of 20 84
Travelling through different materials 16 of 20 84 If you were running along a beach and then ran into the water when would you be moving slower in the water or on the sand? In the water. In a similar way, as light moves from one medium to another of different density, the speed of light changes. Do you think light moves faster or slower in a more dense medium? Light moves slower through a more dense medium.
Bending light 17 of 20 84 The speed of light waves depends on the material they are travelling through. air = fastest glass = slower diamond = slowest If light waves enter a different material (e.g. travel from glass into air) the speed changes. This causes the light to bend or refract. air glass
Why does light change direction? 18 of 20 84 Imagine a car driving from the road into a muddy field. In the muddy field it slows down as there is more friction. If it enters the field at an angle then the front tyres hit the mud at different times. Tyre 1 hits the mud first and will move more slowly than tyre 2. This causes the car to turn towards the normal. When the car leaves the mud for the road, tyre 1 hits the road before tyre 2 and this causes the car to turn away from the normal. road tyre 1 tyre 2 mud
What happens in refraction: air to glass 19 of 20 84 When light is refracted as it travels from air to glass: angle of incidence > angle of refraction i > r As the light ray travels from air into glass it moves towards the normal. In general, when light rays move from a less dense medium (air) to a more dense medium (glass) they bend towards the normal. i > r air glass
What happens in refraction: glass to air 10of of 20 84 When light is refracted as it travels from air to glass: angle of incidence < angle of refraction i < r As the light ray travels from glass into air it moves away from the normal. In general, when light rays travel from a more dense medium (glass) to a less dense medium (air) they bend away from the normal. If the two surfaces of the block are parallel, then the ray at the start is parallel to the ray at the end. glass air i < r
Why does light change direction? 11of of 20 84 If the car approached the muddy field at an angle of incidence of 0 then both front tyres would hit the mud at the same time. The tyres would have the same speed relative to each other so the direction of the car would not change, it would just slow down.
Refraction in a rectangular block 12of of 20 84
Why does light change direction? 13of of 20 84 When light hits a medium at an angle to the n ormal the light bends in a similar way to that described for the car in a muddy field. Part of the light ray s lows d own before the rest and this causes the change of d. irection If the light enters a new medium along the normal (i.e. angle of incidence = 0 ) then it does not bend because all of the light ray slows down at the s ame t. ime
Effects of refraction 14of of 20 84 Many visual effects are caused by refraction. This ruler appears bent because the light from one end of the ruler has been refracted, but light from the other end has travelled in a straight line. Would the ruler appear more or less bent if the water was replaced with glass?
Apparent depth 15of of 20 84 The rays of light from a stone get bent (refracted) as they leave the water. Your brain assumes these rays of light have travelled in straight lines. image Your brain forms an image at the place where it thinks the rays have come from the stone appears to be higher than it really is. actual location
The Archer fish 16of of 20 84 The Archer fish is a predator that shoots jets of water at insects near the surface of the water, e.g. on a leaf. The Archer fish allows for the refraction of light at the surface of the water when aiming at the prey. The fish does not aim at the refracted image it sees but at a location where it knows the prey to be. image of prey prey location https://www.youtube.com/ watch?v=_6lsxa_fjie
Refraction summary 17of of 20 84 1. When light bends this is called r _. 2. Refraction happens because the light changes s. 3. When light enters a more dense medium (e.g. glass), it bends t the normal. 4. When light enters a less dense medium [e.g. air], it bends a f _ the normal. 5. If the incident ray hits a surface at 0º, no refraction occurs True or false? Remember that the angle of reflection [r] and the angle of refraction [r] use the same symbol. In reflection: i = r In refraction: i r