Light Refraction the bending of a light ray

Light Refraction the bending of a light ray as it passes from one medium to another air glass air light slows down (v<c)

Snell’s Law n 1 sin 1 = n 2 sin 2 = angle to the normal (0) n = refractive index (no unit)

Ph. ET Bending light applet

Partial reflection (inverted) Refraction 1 Refraction 2

Refraction Island off Jaffna Sri Lanka

Refraction The waves slow down (bunch up) in the shallow water. Fast Deep Slow Shallow

Fast Deep Slow Shallow NCEA Standard - harder!

n 1 1 n 2 2 Snell’s law calculates angles of refraction. n 1 sin 1 = n 2 sin 2

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A series of waves are travelling through water in a shallow pool and passes into a deeper region as shown. Sketch the waves as they travel through the deep region. shallow deep 1

DOT line (direction of Wave travel) – Thanks to Michael Hatton shallow deep

Deep water Shallow water

Roy and Sally spent time on a beach watching the incoming waves. The diagram below shows wavefronts as they approach shallow water. The waves travel slower in shallow water Copy the diagram and draw an arrow showing the wave direction and the refracted wavefronts in the shallow region Clearly explain why the waves behave as you have drawn them in the diagram above. Deep water 2 NZQA 90254 2006 Shallow water Deep water Shallow water normal The part of the wave front that hits the shallow region slows down and moves at a slower speed through the shallow water. The part of the wave front that is still in deep water is still moving at the same fast speed. It is the different speeds of the wave front that causes the wave to swing towards the normal

or The right-hand end of the waves slow down before the left-hand end. This causes the wave front to swing towards the normal.

The part of the wave front that hits the shallow region slows down and moves at a slower speed through the shallow water as shown in the diagram. 1. • • State what happens to the frequency and wavelength of the waves as they pass from deep to shallow water. NZQA 90254 2006 Shallow water Deep water normal The frequency stays the same Wavelength decreases as speed decreases because frequency equals velocity ÷ wavelength. i. e. , re arranged from v = f There are 8 complete waves passing a fixed point in 20 s. 2. Calculate the frequency of the waves. 3. State two possible units for frequency Hz or 4. The speed of the waves in shallow water is 2. 8 m s– 1. Calculate the wavelength of these waves s-1

3 assume f 1 = f 2 !