1.3 analysing refaction of waves
TRANSCRIPT
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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?