Wave InteractionsWave Interactions

Can you see me now?Can you see me now?

• Transparent materials allow waves to pass through them with little or no distortion

• Translucent materials allow waves to pass through them with varying degrees of distortion

• Opaque materials do not allow waves to pass through them– Waves must be reflected or absorbed

CategoriesCategories

• Reflection

• Refraction

• Diffraction

• Absorption

• Interference– Constructive Interference– Destructive Interference

ReflectionReflection

• Reflection is when a wave bounces off of a surface– Some of the energy may be absorbed, but

most is reflected

• LAW OF REFLECTION– The angle of incidence MUST EQUAL the

angle of reflection

Mirror, mirrorMirror, mirror

• Explains why a mirror must be smooth– So that all the angles line up to make a clear

picture in the reflection– Water surfaces may not be smooth, produce a

distorted reflection

Mirror, etc.Mirror, etc.Chalkboard, Chalkboard,

etc.etc.

Shaped MirrorsShaped Mirrors

• Concave– “caved in”– Light rays, etc., converge in the center– Make the image larger or focus energy

• Parabolic dishes– Satellite dishes– Lighting the Olympic Torch

Shaped MirrorsShaped Mirrors

• Convex– “curved out”– Light rays, etc., spread out from the center– Images look smaller, but cover more area

RefractionRefraction

• Refraction is when a wave bends as it moves from one medium to another– “Edges” of the wave “slow down” in a more

dense medium and “speed up” in a less dense medium

– The wave front bends towards the normal in a more dense medium, and

– away from the normal in a less dense medium

Refraction can depend on the angle Refraction can depend on the angle the wave hits the mediumthe wave hits the medium

Oil-slick RainbowsOil-slick Rainbows

• Because of the different densities of oil, gasoline, water, and air, a rainbow-like refraction can form in puddles near well-traveled parking lots

LensesLenses

• Controlling the “bend” of the light allows us to make lenses

DiffractionDiffraction

• Bending of waves around a barrier

With two barriers, BOTH edges bend the waves

Jetties are false walls to bend the Jetties are false walls to bend the ocean waves towards the shoreocean waves towards the shore

InterferenceInterference

• Whenever two waves of the same kind pass through each other, they interfere

• Constructive Interference– If their crests and troughs line up, they are

said to be “in phase”

• Destructive Interference– If these points don’t, they are “out of phase”– Should they be exactly “out of phase”, the

waves will cancel each other out