14.2 Wave Properties

Mechanical Waves Waves that require a medium Sound, water, in air, on a Slinky These waves are governed by Newton’s laws

Wave pulse a single bump or disturbance that travels through a medium Periodic Wave a wave that moves up and down at the same rate

transverse wave longitudinal wave a wave in which the particles of the medium move perpendicular to the direction of the energy longitudinal wave a wave in which the particles of the medium move parallel to the direction of the energy

surface wave a wave where the particles of the medium move both parallel and perpendicular to the direction of the energy

Amplitude The maximum displacement from rest position more amplitude will take more energy

crest-highest point of a wave trough-lowest point of a wave

Measuring a Wave Wavelength, l, Measured in m, cm, mm, nm The distance from crest to crest or trough to trough

Phase Any two points on a wave that are at least a wavelength apart are in phase. Points that move opposite are 180o out of phase Points can be any where from 0o to 180o out of phase

Period (T) measured in seconds(s) the time for one cycle frequency (f) measured in Hertz (Hz) the number of cycles per second or (reciprocals)

Speed or Velocity Speed (v) measured in m/s The speed of the wave v = lf v = d/t

Remember Amplitude of a mechanical wave determines the amount of energy The medium determines the speed of a wave

14.3 Wave Behavior Two particles cannot be in the same place at the same time. But waves can be. Waves can transfer two different energies through the same space and the same time.

Incident wave is the original wave from the source of disturbance Reflected wave is the wave that bounces off of a boundary

Superposition of Waves Principle of superposition the displacement of a medium caused by two or more waves is the algebraic sum of the displacements caused by the individual waves Interference is the result of superposition

Constructive Interference When the displacement of the waves are in the same direction. The resultant wave amplitude is larger than any individual wave

Destructive Interference Complete destructive interference would be the exact amplitude, but in opposite direction, wavelength and speed Results would be no transfer of energy Destructive interference is not always complete

Standing Wave Node Antinode point of a wave that is not moving the point of maximum displacement

Interference of two waves traveling in opposite direction with the exact same wavelength and opposite amplitudes Energy reflected back and forth and is “standing” in the wave

Waves in Two Dimensions Normal line drawn perpendicular to the barrier angle of incidence the angle between the incidence ray and the normal

Angle of Reflection Law of Reflection the angle between the reflected ray and the normal Law of Reflection the angle of incidence equals the angle of reflection

Refraction of Waves The type of media determines the speed and the wavelength The frequency remains unchanged when the wave moves from one medium into another

v=fl If the medium causes the wave to slow down and frequency doesn’t change what happens to the wavelength?

If the medium causes the wave to speed up what happens to the wavelength? If the waves go from one medium into another at an angle to the two mediums then there is a bending of the wave.

This bending is called refraction. What happens to the angle of refraction if the wave speed increases? Decreases?