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ObjectivesRecognize and describe the properties of:
� Wave reflection
� Wave refraction
� Wave diffraction� Wave diffraction
Each of these is a Big IdeaBig Idea
Wave Reflection
Where have you experienced waves reflecting?
� Echoes
� Radio wavesRadio waves
Wave Reflection
� Waves at right angles
�Waves at oblique angles
�Waves at oblique angles
Wave Reflection
Angle of Incidence
Incident Ray
Angle of Incidence
Angle of
Reflection
Reflected Ray
Wave Refraction
Where do waves move from one medium to another?
� Sound from cold air to warm air� Sound from cold air to warm air
� Light from space to air
� Light from air to water
Wave Refraction� Water passes from deep water to shallow water -
Wavelength shortens
Wave Refraction
When waves move from one medium to another, two things happen:
1. The wave velocity changes1. The wave velocity changes
2. The wave direction changes
Wave Refraction
� Recall the universal wave equation:v = f * λ
In Medium 1 - f1=v1/λ1In Medium 1 - f1=v1/λ1
In Medium 2 -
� No matter what the medium the frequency doesn’t change:
f1 = f2
� Therefore we get:v1/λ1 = v2/λ2
Wave RefractionSpeed of Sound:
� Sound wave speed changes depending on air temperature
v = 331m/s + (0.59 * T)vSOUND = 331m/s + (0.59 * T)vSOUND ~ 330m/s
� Does sound move faster or slower in cold air?
Wave Refraction� Oblique waves bend
towards the normal when entering slower medium
Normal
Normal
� Oblique waves bend away from the normal when entering faster medium
� Oblique waves bend away from the normal when entering faster medium
Wave RefractionWhen waves enter shallow water (lower speed medium)
they bend towards the normal (become more parallel to shore)
Wave Diffraction
Wave Diffraction
Wave Diffraction� Shorter incident
wavelengths are diffracted less
� Longer incident wavelengths are diffracted more
� Longer incident wavelengths are diffracted more
Wave Diffraction� Waves passing through smaller openings are diffracted more
� Waves passing through smaller openings are diffracted more
� Waves passing through larger openings are diffracted less
diffracted morediffracted more
Wave Diffraction
Short wavelengths
diffract less
around an object
Short wavelengths
diffract less
around an object
Long wavelengths
diffract more
around an object
Long wavelengths
diffract more
around an object
Summary� Incident/reflected rays are perpendicular to wavefronts� Angle between incident ray & normal = angle of incidence� Angle between reflected ray & normal = angle of reflection� Angle of incidence = angle of reflection� Waves refract when traveling from 1 medium to another� Waves refract when traveling from 1 medium to another� v1/λ1=v2/λ2� Oblique incident rays bend towards normal when entering a
slower medium� As wavelengths become longer they are diffracted more� As an opening becomes larger, waves passing through diffract
less� Particles do not bend around corners, but waves do
Homework� Reflection, Refraction, and Diffraction
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