Wave Interactions Chapter 15.3 Notes

Section Overview Reflection occurs when a wave meets a surface or boundary and bounces back Diffraction occurs when a wave passes the edge of an object or passes through an opening and the wave bends Refraction occurs when a wave passes from one medium to another at an angle and it bends

Reflection Reflection is simply the bouncing back of a wave when it meets a surface or boundary Examples: when a light strikes a shiny surface, it reflects off of it; water waves hit the side of a boat and are reflected

Diffraction When waves pass the edge of an object, they spread out as if a new wave were created there The same effect occurs when waves pass through an opening, like a window or door Waves bend around an object or opening—known as diffraction The amount of diffraction depends on its wavelength and on the size of the barrier or opening

Refraction Bending of waves when they pass from one medium into another is called refraction Refraction is why a spoon in a glass of water looks like it is broken in two pieces Light that reflects from the spoon handle passes through the glass, through air, and to your eye Light from the spoon in the bottom of the glass passes through the water, through the glass, through air, and to your eye Each time waves enter a new medium, they bend slightly because they travel at a slightly different speed

Interference Waves can share space with other waves When several waves are in the same location, they combine to produce a single, new wave that is different from the original waves This type of wave interaction is called interference

Constructive Interference When the crest of one wave overlaps the crest of another wave (or when the trough of one wave overlaps the trough of another wave) the waves reinforce each other When the waves overlap, the result is a wave whose amplitude is the sum of the amplitudes of the two individual waves

Destructive Interference When the crest of one wave meets the trough of another wave, the resulting wave has a smaller amplitude than the larger of the two waves For example: imagine that the crest of one wave has an amplitude of 4 cm, and the trough of another wave has an amplitude of 3 cm If the crest and trough overlap, the resulting wave will have an amplitude of just 1 cm If destructive interference occurs between two waves with the same amplitude, the waves may completely cancel each other out

Interference of Light Waves The interference of light waves can create colorful displays For example, soap bubbles appear many different colors due to the interference patterns of different light waves Some light waves strike a soap bubble and bounce off the outside directly back to your eye; other waves bounce off the inner side of the bubble, travel back through the shell, and then into your eye When waves constructively interfere, they are in phase and create colors When waves destructively interfere, they are out of phase and create different colors—result of waves interfering in different ways is a swirling rainbow effect

Interference of Sound Waves Sound waves from two tuning forks of slightly different frequencies will interfere with each other When compressions arrive at your ear at the same time, constructive interference occurs and the sound is louder When a compression and a rarefaction arrive together, destructive interference occurs and a softer sound is heard Within the overall sound, you hear a pattern of alternating loud and soft sounds, called beats

Standing Waves A standing wave results from interference between a wave and its reflected wave It causes the medium to vibrate in a stationary pattern that resembles a loop or a series of loops Each loop of a standing wave is separated from the next loop by points that have no vibration, called nodes Nodes are where crests of the original wave meets the troughs of the reflected wave—they are points of complete destructive interference Midway between the nodes lie points of maximum vibration, called antinodes Antinodes form where the crests of the original wave line up with the crests of the reflected wave—complete constructive interference occurs