Wave Phenomena Characteristics of Waves

What is a wave? G A wave is a vibratory disturbance through a material (medium) or space G Waves transfer ENERGY without transferring mass G A wave is a vibratory disturbance through a material (medium) or space G Waves transfer ENERGY without transferring mass

Classifying Waves 1. Electromagnetic waves G No medium required G Travel at the speed of light G c = 3 x 10 8 m/s G Examples: visible light, x-rays, infrared G Reference Table: Electromagnetic spectrum G No medium required G Travel at the speed of light G c = 3 x 10 8 m/s G Examples: visible light, x-rays, infrared G Reference Table: Electromagnetic spectrum

2. Mechanical Waves G A. Longitudinal waves - vibrate parallel to wave motion G Examples - sound, seismic s-waves G A. Longitudinal waves - vibrate parallel to wave motion G Examples - sound, seismic s-waves Require a medium ex. Sound, water, waves in springs G B. Transverse waves - vibrate perpendicular to wave motion G Examples: light, seismic p-waves, water

Transverse or longitudinal? Longitudinal Transverse

G What is a pulse? How can we describe its motion? Pulse Periodic wave A pulse is a single vibration moving at constant speed

Important G Speed of a wave or pulse doesn’t change unless the characteristics of the medium change

Periodic Waves G Sketch:

frequency (f): number of vibrations per unit time units: hertz (1 hertz = 1 cycle per second) period (T): time required for 1 vibration units: seconds equation:

wavelength ( ): distance between two points in phase units: meters

phase: G points on wave having the same displacement from rest position AND moving in the same direction (up or down only) are in phase Examples: A & E & I, B & F, C & G, D & H

speed:  units: m/s

amplitude: maximum displacement of a particle from rest position

G Examples: L = 3m v = 12 m/s f T 6 m 3 m 2 m v = f T=1/f 2 Hz 4 Hz 6 Hz.5 s.25 s.17 s

Relationship between T, f and G As frequency increases (at constant velocity), what happens to wavelength? G decreases G As frequency increases, what happens to period? G decreases G As frequency increases (at constant velocity), what happens to wavelength? G decreases G As frequency increases, what happens to period? G decreases

Doppler Effect G Change in “apparent” frequency caused by relative motion between a source and an observer Object moving toward you shorter higher f Object moving away from you longer lower f

Examples: G 1. Sound - train whistle - higher pitch as it moves toward you, lower pitch as it moves away. G 2. Light - Red Shift –Evidence of Big Bang Theory - as universe expands, stars move away, larger wavelength and smaller frequency - shift toward red end of spectrum G 1. Sound - train whistle - higher pitch as it moves toward you, lower pitch as it moves away. G 2. Light - Red Shift –Evidence of Big Bang Theory - as universe expands, stars move away, larger wavelength and smaller frequency - shift toward red end of spectrum

Point sourceLine source What is a wave front? Adjacent points on a wave that are in phase with each other

G Wave fronts for a moving object: Point source - stationaryPoint source -moving

What happens to a wave when a new medium is encountered? G Frequency from the source is constant G Since v = f, if velocity changes, then wavelength changes G Wave can be reflected, transmitted through a new medium, or absorbed by the new medium G Frequency from the source is constant G Since v = f, if velocity changes, then wavelength changes G Wave can be reflected, transmitted through a new medium, or absorbed by the new medium

How can we describe wave interference? G Two or more waves pass through the same region - original wave is unchanged

G Constructive interference- two crests meet, or two troughs meet G Maximum when phase difference is 0° or 360° (360° is a whole wave) G Destructive interference - crest meets trough G Maximum when phase difference is 180° (180° is half of a wave) G Constructive interference- two crests meet, or two troughs meet G Maximum when phase difference is 0° or 360° (360° is a whole wave) G Destructive interference - crest meets trough G Maximum when phase difference is 180° (180° is half of a wave)

Constructive or Destructive? Destructive - 180° out of phase

Constructive or Destructive? Constructive - 0° or 360° (in phase)

Constructive or Destructive? Both constructive and destructive

Law of Superposition G Resultant displacement is the algebraic sum of the displacements due to the individual waves

The red wave is the resultant wave.

G What will the resultant wave look like?

What are standing waves G Two waves of the same frequency and amplitude moving in opposite directions Nodes - points that appear fixed Antinodes (modes) - points of maximum amplitude above and below rest position

Sketches: L 2L L L/2 2/3 L /2 3/2 2 How are the number of nodes related to the number of antinodes? N = A + 1