1.3 Analysing Refaction of Waves

8/2/2019 1.3 Analysing Refaction of Waves

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REFRACTION

The change in direction ofpropagation of wave (bending)orthe change in speed that occurs

when waves (such as light or

sound waves) crosses the

boundary between the twomedium of different density//different depth.


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Plane water wavesin a ripple tank


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A plat piece of plastic/glassmakes the water more shallow.

This slows the waves down.When they slow, they changedirection. This bending effect is

called refraction.


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When a wave encounters different

depth where the wave speed isdifferent, the wave will changedirections.

Notice that as the wave fronts crossthe boundary the wavelength

changes, but the frequency remainsconstant.


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The refraction of water waves

occur when the wave move fromthe different depth of water.

Depth v f

Increase Decrease Increase constant

Decrease Increase Decrease constant


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The direction and the shape of the refracted wave depends on the shape of the

boundary of the different depth.

(i)

(ii)

(iii)

(iv)

(v)

deep

deepdeep

deepdeep

deepdeep

deepdeep

deepshallow

shallow

shallow

shallow

shallow


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Light waves


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In the broken pencil illusion

below right the glass blockbends the light as it enters and

leaves it.

The bending effect is calledrefraction.


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The light travels from less dense medium

(air) to denser medium (water).

Refracted ray bent towards normal line:

2 < 1


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Sound wave


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During the night time, when the ground

cools quickly air near the ground

becomes colder than that above. Sound

waves travel more slowly through this

colder air. So, waves leaving the ground

tend to bend back toward its, instead of

spreading upwards the bending effect iscalled refraction.


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Question 2 (Problem Solving)

Figure (a) and (b) show a tall straight, sided mug and a coin at the bottom.

(a) What would you do to make the coins appear without touching anything.

__________________________________________________________

[1 mark]

(a) Draw the ray from coin reach the eye so you can see the image of the coin. [3 marks]


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Marking scheme

(1) a. State the differences between figure (a) and (b)

wavelength // symbol

b. Relate the relationship between depth and wavelength

When depth increases, wavelength increases. // vise versa

c. State the relationship between depth and speed and frequency.

(i) decrease

(ii) constant

d. State the name of the phenomenon.

refraction

(2) a. State the coin appears without touching anything

Put water / / any liquid

b. Draw the ray from eye to the coin.


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What happen when travel light travel fromthe air and passes through water?

What happen when water waves

propagates from deeper part to shallowerpart?

What happen when sound travels from

higher densities of air to lower densities?

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1.3 Analysing Refaction of Waves