# Waves.

## Presentation on theme: "Waves."— Presentation transcript:

Waves

Waves do NOT carry matter
Disturbances All waves carry energy Waves displace matter Waves do NOT carry matter

Medium Medium – the material a wave travels through
When sound travels through air, the air is the medium When sound travels through a solid, such as glass, the glass is the medium

Types of Waves

Transverse Waves Examples: water waves, light waves, waves in a string or a rope, secondary seismic waves Displace the medium perpendicular to the direction the wave travels

Crest Wavelength amplitude Trough

Longitudinal Waves (compression waves)
Example: sound waves, primary seismic waves Displace the medium parallel to the direction the wave is moving

(Wave animation)

amplitude compression wavelength rarefaction

Wave Interactions

Reflection A wave “bounces back” when it encounters a new medium
Law of reflection: the angle of reflection equals the angle of incidence

Reflection Reflection from a fixed boundary
Reflection from a soft boundary

Some Uses of Reflection

Refraction A wave changes speed and direction (bends) when it enters a new medium Waves travel at different speeds in different mediums (due to density differences) When a wave strikes the boundary between mediums at an angle, one part of the wave slows down before another, and the wave bends Refraction animation -

Light reflected from fish is bent as it travels from water into the air. To the viewer, it appears as if the fish is along a straight line (the refracted ray)

Diffraction A wave bends as it passes around a barrier
Used in spectroscopy (learning about the universe from the colors of light emitted from objects)

Interference Two or more waves combine
Because waves are not matter (they are disturbances that displace matter), more than one wave can occupy the same space at the same time This is called superposition

Interference (continued)
When two crests meet, their amplitudes are added (constructive interference) When a crest and a trough meet, their amplitudes cancel each other out (destructive interference) The resulting wave is the sum of the amplitudes at all points

Constructive and Destructive Interference

Superposition of Waves

Constructive and Destructive Interference

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