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11-3: PROPERTIES OF WAVES. Wave Motion. A wave is a disturbance created by a vibrating source. Two types of waves Electromagnetic or Mechanical Electromagnetic waves can travel through space Mechanical waves require a material medium.
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Wave Motion • A wave is a disturbance created by a vibrating source. • Two types of waves • Electromagnetic or Mechanical • Electromagnetic waves can travel through space • Mechanical waves require a material medium.
As a wave propagates, particles in the medium vibrate about an equilibrium position.
Wave Types • Pulse - is a single non periodic disturbance. • Periodic wave - a wave whose source is undergoing some form of periodic motion.
Transverse waves • Particles vibrate at right angles to the direction of propagation. • Crest – the highest point above the equilibrium position • Trough – the lowest point below the equilibrium position • Wavelength – the distance between two adjacent similar points of the wave, symbol =
Longitudinal waves • Particles vibrate parallel to the direction of wave motion. • Thecrests of the wave corresponds to the compressed regions, and the trough corresponds to the stretch regions
Frequency & Period • The frequency of a wave is the number of crests that pass a point in a given time (usually in hertz). • The period is the time required for the wave to travel one wavelength (two successive crests).
Wave Speed • The relationship between the frequency and wavelength of a wave is given by the wave equation: • Energy carried by a wave depends on the amplitude at which the particles of the medium are vibrating. As the amplitude increases so does the energy the wave carries
Sample Problem • The string of a piano that produces the note middle C vibrates with a frequency of 264Hz. If the sound waves produced by this string have a wavelength in air of 1.30 m, what is the speed of sound in air?
Solution • Given: • Frequency = 264 Hz • wavelength = 1.30 m • v = ? • v = frequency x wavelength • = 264 Hz x 1.30 m • = 343 m/s
Sample Problem • 2 boats are anchored 4 m apart. They bob up & down every 3 s. When one is up, the other is down. There are no crests between them. Determine the speed of the waves.
½ = 4 m • = 8m • f = 1/T = 1/3s = 0.33 s-1 • v = f • = (8m)(0.33 s-1) = 2.7 m/s
Superposition • Superposition is the idea that two waves can occupy the same space at the same time. • Superposition principle: when two or more waves travel through a medium, the resultant wave is the sum of the displacements of the individual waves at each point.
Once the waves pass through each other each wave proceeds independently.
Constructive Interference • Results when 2 waves meet up exactly crest to crest ( in phase). This produces a pulse of greater amplitude than either of the original waves.
Destructive Interference • Results when two waves meet exactly crest to trough ( out of phase). • If the individual waves have the same amplitude the resultant wave will equal zero.
Standing Waves • Wave pattern that results when two identical waves travel in opposite directions and interfere.
Node: point in a standing wave that always undergoes complete destructive interference and therefore is stationary • Antinode: point in a standing wave, halfway between two nodes, at which the largest amplitude occurs
Only certain frequencies produce standing waves. • The wavelengths depend on the string length. • Possible wavelengths include 2L, L, and (2/3)L