Waves and Sound

Waves and SoundChapter 16

16.1 The Nature of Waves

A Wave:1. Traveling disturbance2. Carries energy from place to place

Two Different Types:3. Transverse4. Longitudinal

Slinky

• If the end is jerked up and down, an upward pulse is sent traveling toward the right.

• If the end is then jerked down, a downward pulse is generated and also moves to the right.

Transverse Wave

• Wave in which the disturbance occurs perpendicular to the direction of travel of the wave.

Ex. Radio waves, light waves, microwaves, guitars and banjo strings

Longitudinal Wave

• The disturbance occurs parallel to the line of travel of the wave.

• Ex. Sound wave

Transverse and Longitudinal

• Some waves have both.• Water waves• Particles at the surface move on nearly

circular paths.

16.2 Periodic Waves• Transverse and longitudinal waves are types of periodic

waves.• Cycles or patterns that are produced over and over again

by the source.• Cycle: • Amplitude A: maximum excursion of a particle of the

medium from the particle’s undisturbed position. Distance between a crest, or highest point on the wave pattern, distance between a trough, or lowest point on the wave pattern.

• Wavelength: horizontal length of one cycle of the wave, horizontal distance between two successive crests.

• Period T: time required for one complete up/down cycle, just as it is for an object vibrating on a spring. Time required to travel one wavelength.Frequency: cycles per second or Hertz Hz

Example

Ex. One cycle of a wave takes one-tenth of a second to pass an observer, then ten cycles pass the observer per second.

F = 1/(0.1s) = 10 cycles/s = 10 Hz

Train example

• Fig 16.6• Train moves by at a constant speed v. The train consists

of a long line of identical boxcars, each of which has a length and requires a time T to pass, so the speed is

v = /T Same equation applies for a wave and relates the speed of the wave to the wavelength and the period T. Since the frequency of a wave is f = 1/T, the expression for the speed is

Example 1: The Wavelengths of Radio Waves

• AM and FM radio waves are transverse waves consisting of electric and magnetic disturbances traveling at a speed of 3.00 x 10^8 m/s. A station broadcasts an AM radio wave whose frequency is 1230 x 10^3 Hz (1230 kHz on the dial) and an FM radio wave whose frequency is 91.9 x 10^6 Hz (91.9 MHz on the dial). Find the distance between adjacent crests in each wave.

The distance between adjacent crests is the wavelength . Since the speed of each waves is v = 3.00 x 10^8 m/s and the frequencies are known, the relation v = f can be used to determine the wavelengths.

Slinky Experiment

HOMEWORKPg. 5041, 2, 3, 4, 5

Terminology

Crest: the top of a waveTrough: the bottom of a waveAmplitude: how far the material is displaced from

rest (from crest to trough)Wavelength: the length of one full wave (between

two identical points, like two crests)Speed: how fast the wave movesFrequency: how many waves there are in a certain

amount of time.