Section 3

Behavior of Waves

Key Concepts• How does reflection change a wave?• What causes the refraction of a wave

when it enters a new medium?• What factors affect the amount of

diffraction of a wave?• What are two types of interference?• What wavelengths will produce a standing

wave?

Reflection• The bouncing back of a wave after it strikes a

boundary that does not absorb all the wave’s energy

• Angle of incidence = angle at which the wave hits the boundary

• Angle of Reflection = angle at which the wave bounces off the boundary

• Angle of Incidence = Angle of Reflection• Reflection does not change the speed or

frequency of a wave, but the wave can be flipped upside down.

Refraction• The bending of waves due to a change in

speed.• Occurs because waves move at different

speeds through different mediums.• When a wave enters a medium at an

angle, refraction occurs because one side of the wave moves more slowly than the other side.

Refraction

Refraction

Diffraction• The bending of waves around the edge of

an obstacle• Diffraction is the result of a new series of

waves being formed when the original waves strike an obstacle.

• A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle.

Interference• When two waves arrive in the same place at the

same time, they interact• There are two types of interaction:• Constructive Interference – waves combine in

such a way that the disturbance that results is greater than either wave alone

• Destructive interference – waves combine in such a way that the disturbance that results is less than either wave alone

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Standing Waves• A wave that does not appear to be moving• Two parts of a Standing Wave• Nodes: where destructive interference results in

no energy displacement• Antinodes: where constructive interference

causes maximum energy displacement• A standing wave forms only if half a

wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord.

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Reviewing Concepts• 1. How is a wave changed by reflection?• 2. What causes refraction when a wave

enters a medium at an angle?• 3. What determines how much a wave

diffracts when it encounters an opening or an obstacle?

• 4. List the types of interference.• 5. At what wavelengths can a standing

wave form in an elastic cord?