Refraction

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Refraction

The car travels on the path shown. When the surface changes from road to mud its direction changes.

Draw the diagram and explain why the car’s direction changes.

Refraction• Objective: Pupils will be able to...

C: describe the changes in a wave when it is refractedB: predict how a wave will behave when its speed changesA: compare information to decide if light speeds up or

slows down when changing mediums• Outcome: Pupils will show...

– a change of speed can affect direction– a change in direction can be used to decide if speed is

increasing or decreasing– where and why light changes speed– what changes when a wave changes speed

Questions• Draw what will happen when the car travels from:

– Mud to Road– Mud to Snow

• Explain:– Is the car speeding up or slowing down?– Which tyre will be affected first?

Medium Speed

Road Fastest

Mud Medium

Snow Slowest

• mud to road• speeding up• The right tyre

hits first, speeds up and pushes the car left.

• mud to snow• slowing down• The right tyre

hits first, slows down and pulls the car right.

• WRONG• It shows the car slowing

down, which is right.• But the car cannot double

back on itself. Even if the right tyre nearly stops when it hits the new surface, when the left tyre gets on the new surface they will travel at the same speed.

• TRY IT!!!!!!!

• Where does light travel faster, air or water?– Hints:• The light goes from the penny to the eye.• Think about the car, which tyre hits the air first.• Does the tyre speed up or slow down?

• Arrange water, air and diamond from fastest to slowest.• Explain the pattern using ideas about particles.

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Refraction

• Does the light wave speed up or slow down as it travels from air to glass?• Explain using the path of the light (and the tyres).• Explain using ideas about particles.

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=16

• When a light wave refracts, what changes?

DirectionSpeedWavelengthFrequency

Arrange the states of matter from fastest to slowest and complete the table, including diagrams.

States of Matter Speed Diagrams

As density increases, the speed of lighta)increasesb)decreasesc)remains constant

Summary:Explain, using the car analogy, how you can predict the behaviour of light when it changes medium.

Refraction Level AssessmentC: How does filling the beaker with water affect the way we see the penny at the bottom

of the beaker. Include a diagram.• keywords: increase, decrease, remain constant, wavelength, frequency, direction,

wavespeed, crest, troughB: Explain how the changes of the wave’s properties caused this observation. Diagram

two examples: one of a wave travelling from air to glass and one from water to air.• keywords: waves, accelerating, decelerating, particles, solid, liquid, gasA: Use the examples of light that you have just created to compare the differences of light

and sound. • keywords: concentration, density, transverse, longitudinal, solid, liquid, gasA*: Refractor telescopes use convex lenses rather than concave lenses. Use diagrams to

show how light rays are affected by the different lenses. Research or predict the uses of concave lenses.

• keywords: concave, convex, wavespeed, accelerating, decelerating

C: 1. When a light wave refracts, which of the wave’s properties does not change: speed, direction, frequency or wavelength?

B: 2. Does light travel faster in solids, liquids or gases? Why? (Include particle diagrams.)

3. Draw a car travelling from mud to road. Explain why the car changes direction. Which tyre hits the road first and does it speed up or slow down.

A: 4. Draw light travelling from air to glass. Explain why the light changes direction by talking about which side of the wave hits the glass first: think about the tyres. (Include particle diagrams.)

5. Draw light travelling from water to air. Explain why the light changes direction by talking about which side of the wave hits the glass first: think about the tyres.. (Include particle diagrams.)

A* 6. Make a large diagram of a convex lens with five light rays travelling into it: predict what happens to the direction of the light.

7. Make a large diagram of a concave lens with five light rays travelling into it: predict what happens to the direction of the light.

8. Sometimes when people use convex lenses the image appears upside down. Why?