Oscillations and Waves

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Oscillations and Waves

• Wave Properties

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• Reflection and Refraction
• Terminology (define these in your own words)
• Incident ray
• Reflected ray
• Refracted ray
• Normal line
• Angle of incidence / reflection / refraction
• Interface or boundary
• Law of reflection
• angle of incidence angle of reflection

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Refraction This is caused by a change in speed as
a wave passes form one medium into another. It
results in - change in direction - change in
wavelength ( as v f? )
When there is refraction of a wave such as light,
part of the wave is also reflected. This results
in a decrease in intensity of the transmitted
(refracted) wave.
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Refractive index The degree of refraction of
light at a boundary is measured by the refractive
index, n. The greater the reduction in speed of
the light, the greater the refractive
index Experiment Investigate the
relationship between the angle of incidence and
angle of refraction for light.
nm absolute refractive index of a medium, m
(no unit) c speed of light in a vacuum vm
speed of light in medium
nm c vm
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Snells Law It can be shown that the relative
refractive index of two materials is given by the
formula
Material 1
Material 2
Where light travels from material 1 into material
2. Here i angle of incidence r angle of
refraction
1n2 sin i sin r
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In the data booklet the angles of incidence and
refraction are called ?1 and ?2. It can further
be shown that Note that this is written in
the data booklet as

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• E.g. 1
• A wave travelling at 12cms-1 is incident upon a
  surface at an angle of 55 from the normal.
• If the angle of refraction is 40, determine the
  speed of the wave in the second medium.
• If the initial wavelength is 6cm determine the
  frequency of the wave in the second medium.

In first medium v f? f v/? 0.12 /
0.06 2.0 Hz Frequency does not change during
refraction ? f 2.0 Hz
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E.g. 2 For light travelling from water into
glass, r20. If nw 1.33 and ng 1.50,
determine i (?1).
sin20 1.33 sin?1 1.50
sin?1 0.34 / 0.89 0.38 ?1
sin-1 0.38 22.5
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Phase and Wavefronts If two oscillating bodies
are in phase, this means that they reach their
maximum displacement at the same time. E.g. any
two wave crests are in phase. E.g. During
refraction of a water wave (Youtube link)
A wavefront is a line joining adjacent points
that are in phase.
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Diffraction When a wave passes through a gap or
edge of a barrier they spread out. This effect
is called diffraction. (You tube link)
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Superposition (interference) Whenever two waves
of the same type meet at the same point, the
total amplitude (displacement) at that point
equals the sum of the amplitudes (displacements)
of the individual waves. (You tube link1 and
link2)
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For constructive interference at any point,
wavefronts must be in phase and their path
difference must be a whole number of
wavelengths path difference n? For
destructive interference at any point, wavefronts
are p out of phase and their path difference is
given by path difference (n ½) ?
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• Task On your interference diagram
• Draw in lines of constructive and destructive
  interference
• Indicate the lines that join points
• a. in phase
• b. 2p out of phase (path difference ?)
• c. 4p out of phase (path difference 2?)
• d. 3p out of phase (path difference 1.5?)

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Coherent waves A stable pattern of interference
is only obtained if the two wave sources are
coherent. Two coherent wave sources i. have a
constant phase difference, ii. thus produce
waves with equal frequency.
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• Superposition links
• - PheT Sound (see jar file)
• Superposition of two pulses
• With editable wave equations
• Creating a standing wave

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