Refraction

All waves can be 'refracted' - its a fancy way of saying 'changing direction'

What does refraction mean? [1]
- When waves change direction as they enter a different medium (a substance with a different optical-density)
  - Why do waves change direction as they enter a different medium? [1]
    - This is caused entirely by the change in speed of the waves
      - Why do waves change speed in different mediums? [1]
        
        EM waves travel more slowly in denser media (usually)
        
        What type of waves travel faster in denser substances? [1]
        
        Sound waves
      - How does changing speed cause a change in direction? [2]
        
        If a wave meets a different medium at an angle, this part of the wave hits the denser layer first and slows down...
        
        ...while the other part carries on at the faster speed

When light shines on a glass window pane, some of the light is reflected, but a lot of it passes through. Does this light get refracted? [1]
- Yes - Since the light is passing from air (medium 1) into glass (medium 2)
  - How does the light change speed as it passes from the air (a less optically-dense medium) into glass (a more optically-dense medium)? [1]
    - It slows down
      - Which way does the light bend? [1]
        
        Towards the normal
  - How does the light change speed as it reaches the 'glass to air' boundary on the other side of the window? [1]
    - It speeds up
      - Which way does the light bend? [1]
        
        Away from the normal
Why do ponds look shallower than they really are? [1]
- Light is refracted when it leaves the water, making the pond floor look nearer than it is
- - How does the light change speed as it passes from the water (denser medium) into the air (less dense medium)? [1]
    - It speeds up
      - Which way does the light bend? [1]
        
        Away the normal
Why do triangular prisms create a spectrum (rainbow effect)? [1]
- White light is made up of different wavelengths (colours) of light
- Different wavelengths (colours) of light refract by different amounts
- As white light passes the prism boundaries, each wavelength (colour) of light refracts slightly differently and they disperse

Classwork
- 1) What does it mean when we say that a beam of light 'refracts' when it enters a different medium?
- 2) Draw a diagram to show the path of a ray of light that travels from air, enters a rectangular block of glass, then exits the block back into air on the other side (use an angle of incidence larger than 0º)
- 3) Make a leaflet / poster about refraction. It should include key diagrams to explain refraction as well as some photos of refraction found in everyday circumstances (e.g. glass of water, swimming pool, rainbow, windows, etc)
Homework
- 1) What causes refraction? Choose one of the following explanations:
  - Refraction is caused by an image being formed at the boundary between two media
  - Refraction is caused by light being reflected off the boundary between two media
  - Refraction is caused by one medium being better able to absorb light than another
  - Refraction is caused by light changing speed as it enters another medium
- 2) Diagrams A and B show waves travelling from an optically-dense medium to a less optically-dense medium
  - Which diagram shows the waves being refracted?
  - Why does refraction not happen in the other diagram?
  - What happens to the wavelength of the waves after they have passed into an optically-denser medium?
  - What happens to the frequency of the waves after they have passed into an optically-denser medium?
  - What happens to the velocity of the waves after they have passed into an optically-denser medium?
  - Imagine that the wave in diagram B passed into the less optically-dense medium again. What would happen to the speed of the wave?

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Refraction

All waves can be 'refracted' - its a fancy way of saying 'changing direction'

What does refraction mean? [1]

When light shines on a glass window pane, some of the light is reflected, but a lot of it passes through. Does this light get refracted? [1]

Why do ponds look shallower than they really are? [1]

Why do triangular prisms create a spectrum (rainbow effect)? [1]

Classwork

Homework