What changes the direction of a wave?
A wave can change direction as a result of
• Reflection
• Refraction
• Diffraction
Reflection
• Reflection occurs when a wave bounces off a surface that it
cannot pass through.
• Reflection does not change the speed or frequency of a wave.
• When reflection occurs at a fixed boundary, the reflected wave is
upside down compared to the original wave.
• An image is a copy of an object formed by reflected or refracted
waves of light.
• Regular reflection occurs when parallel light waves strike a
surface and reflect, all in the same direction.
• Regular reflection occurs when light hits a smooth, polished
surface, such as a mirror or the surface of a smooth body of
water.
• An echo is produced by the reflection of acoustic (sound) waves.
• Diffuse reflection occurs when parallel light waves strike a
rough, uneven surface and reflect in many different directions.
• Light reflecting off of paper is an example of diffuse reflection
since paper has a rough surface.
Refraction
• Refraction is the bending of a wave as it enters a new medium
at an angle.
• Refraction occurs because a wave’s speed changes as it enters a
new medium. When the wave enters a new medium at an angle,
one side of the wave moves at a faster speed than the other side.
• Water waves refract when they enter shallower water at an
angle. In this case, water depth acts like a different medium.
• Light waves refract when the light enters a new medium at an
angle, such as when light travels from air to water.
Diffraction
• Diffraction is the bending of a wave as it moves around an
obstacle or passes through a narrow opening.
• A wave diffracts if its wavelength is large compared to the size of
an obstacle or opening.
• If its wavelength is small compared to the size of an obstacle or
opening, the wave bends very little.
• Scattering is the redirection of light in all directions as it passes
through a medium. For example, light is scattered by small
particles and gases in the air as it passes through the
atmosphere.
• Gas molecules scatter shorter-wavelength blue light more than
the light of longer wavelengths. This explains why the sky
appears blue on a sunny day.