2. Wave Reflection
• A reflection occurs when a wave hits a
surface and bounces off
– All types of waves can be reflected
• sound (echoes)
• light (mirror images)
• water
Powerpoint Templates
3. Angles of Reflection
• The incident wave is
the source of energy;
it shows where the
wave is coming from.
• The normal is an
imaginary line drawn
perpendicular to the
reflective surface.
• Law of reflection:
– the angle of incidence (i) is equal to the angle of
the reflected wave (r).
Powerpoint Templates
4. Reflection and Sight
• How does this woman see her foot in the mirror?
– Light reflects off of her foot, hits the mirror, reflects off
the mirror, and enters her eyes
• The woman's brain
assumes light travels in a
straight line.
– Her brain interprets the
image as being actually
inside the mirror.
Powerpoint Templates
5. Refraction
• As waves travel from one medium to another,
some waves are reflected (bounce back) and
others are refracted ("bent" into a new direction)
• Examples:
– air to glass to air
• Store window
– air to glass to water
• pencil in water cup
– layers of Earth
• seismic waves
– air to water
• The Gar Story
Powerpoint Templates
6. Visualizations of Refraction
As a column of marching troops crosses
Concrete from a fast medium to a slow medium, the
direction of march changes because the
first lines of men to reach the "swamp" slow
down before the others.
Swamp Fast
Medium
As a toy car rolls from a hard floor
onto carpet, it changes direction
because the wheel that hits the carpet Slow
first is slowed down first. Medium
• Refraction occurs when a wave is bent as it passes from one
medium into another due to changing wave speed.
Powerpoint Templates
7. Direction of Refraction
Fast
Medium
normal
• When a wave refracts into a substance in which it must slow down,
the direction will bend towards a line that is perpendicular to the
surface that it strikes (the normal).
• When waves refract into a substance in which they speed up, the
direction will bend away from a line that is perpendicular to the
surface that it strikes. Powerpoint Templates
8. Refraction
• Light waves slow down in a denser
or more solid medium and speed up
with less matter (less dense or less
solid).
• Sound waves speed up in a
denser or more solid
medium and slow down the
less matter there is (less
dense or less solid).
• Refraction simulator
Powerpoint Templates
9. Mirage
• Light and sound both travel
faster in hot air
– hot air molecules move faster
than cool air, transferring the
wave energy along more
quickly
• Layer of hot air near the
ground refracts images of
the sky
• Your brain assumes light
travels in a straight line
• Image appears to you as a
blue wavy spot on the ground
Powerpoint Templates
10. Diffraction
• What happens when waves
encounter obstacles in their
path?
– some waves are reflected
– some waves are diffracted
(waves change direction as
they pass through or around
the obstacle)
• solid object
– boulder in the ocean
– radio waves around a building
• aperture (opening)
– gap in a sea wall
– light through a camera f-stop
– holes in a musical instrument
Powerpoint Templates
11. Diffraction Around an Object
• The amount of direction change (diffraction) around an
object depends on two things:
– the size of the object
• bigger object cause greater diffraction
– AND the size of the wavelength (λ)
• smaller wavelengths cause greater
diffraction
• light waves have very small
wavelengths so they experience
less diffraction than sound or
water waves Powerpoint Templates
12. • When a wave is diffracted, wavelength, frequency, and
speed stay the same
– ONLY WAVE DIRECTION & AMPLITUDE CHANGE
• diffracted sounds are same pitch but not as loud
• diffracted light is same color but not as bright
• diffracted ocean waves are just as frequent but less high
• There is always an area sheltered by waves directly
behind the object
– waves are less intense, but not absent there
– this is why most shadows have a fuzzy edge
Powerpoint Templates
13. Diffraction Through an Aperture
• The amount of curving through an opening depends on
– the size of the opening (a = aperture)
– the relative size of the wavelength (λ)
• If opening is larger than wavelength, curving will be minimal.
• If the two are equal in size or the opening is smaller than the
wavelength, the amount of curving is considerable.
• Diffraction is greatest
when λ ≥ a.
– This happens when:
• the aperture is small
• the wavelength is large
(bigger than aperture)
Powerpoint Templates Demo
14. Useful Diffraction
• In a harbor, only a small section of waves is allowed
to pass through the walls enclosing the bay.
• The waves passing through the gap
are spread out (diffracted) into smaller,
curved waves.
• Any boat or ship floating within the harbor
only experiences very small (dissipated)
waves, despite that fact that the inner water
is exposed to the outside waves through the
gap in the harbor wall.
Powerpoint Templates
16. Interference
• When two waves overlap, interference occurs.
– Waves usually originate from different locations, so they
often travel in different (even opposite) directions
– The resulting wave is the sum of the incoming waves
• two crests will add up to create a higher peak: 1 + 1 = 2
• a crest and a trough will cancel each other out: 1 + (-1) = 0
• Constructive Interference
– wave are "in phase"
– wave forces combine
• Destructive Interference
– wave are "out of phase"
– wave forces cancel out
Powerpoint Templates
17. Examples of Interference
Constructive Interference Optical interference between two light sources.
Destructive Interference
• After waves meet and interference
occurs, they continue on unaffected.
Powerpoint Templates
18. Resonance
• Every object has a natural frequency at which it vibrates
– This is determined by:
• the object's size & shape
• mass of the object
• material the object is made out of
• Resonance occurs when the frequency of a forced vibration applied
to an object matches the object's natural frequency.
– a combination of reflection and constructive interference
Incident Wave
Reflected Wave
Resultant Wave
Powerpoint Templates
