Behavior of Waves

Reflection, Refraction, Diffraction and Interference in waves

Reflection

• Reflection occurs when a wave bounces off of a surface it cannot pass through

• It is like when a ball hits a wall and bounces back

• Reflection does not change the speed or frequency of a wave

• the wave can be flipped upside down if the boundary is fixed

Refraction

• Refraction is the bending of a wave as it enters a new medium at an angle

• When a wave enters a new medium at an angle refraction occurs because one side of the wave moves more slowly than the other

• Refraction occurs only when the two sides of a wave travel at different speeds

Diffraction

• Diffraction is the bending of a wave as it moves around an obstacle or passes through a narrow opening

• If the wavelength is small compared to the opening then the diffraction will be little

• The larger the wavelength compared to the obstacle or opening, the larger the diffraction

Interference

• Interference occurs when two or more waves overlap and combine together

• The two types of interference are constructive interference and destructive interference

• Waves increase in amplitude in constructive interference and decrease in amplitude in destructive interference

Constructive Interference

• Constructive interference occurs when two or more waves combine to produce a wave with a larger displacement

• If two transverse waves meet then the crest will be higher and the trough will be lower according to the amplitude of the two waves

Destructive Interference

• Destructive interference occurs when two or more waves combine to produce a wave with smaller displacements

• Destructive interference of transverse waves will produce a wave with a smaller crest and trough according to the size of the waves meeting each other

Standing Waves

• A standing wave is a wave that appears to stay in one place, it does not seem to go through a medium

• This can be seen if you tie a rope to a chair and shake the other end of the rope, at some point the incoming waves will meet the reflected waves

Nodes and Antinodes

• A node is a point on a standing wave that has no displacement from the rest position

• At the node there is complete destructive interference between the incoming and reflected waves

• An antinode is a point where a crest or trough occurs midway between two nodes

Standing Waves

• 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

• Once you find the frequency that produces a standing wave, doubling or tripling the frequency will also produce a standing wave