Lesson 4C Basic Wave Concepts Oscillations & Waves Lesson 4C Basic Wave Concepts

How Do We Describe Waves?

Pulse A discrete disturbance propagated through a medium

Wave Train Generating a repeated sequence of pulses produces a continuous waveform

Longitudinal Wave Features Compression – a region of higher-than-normal density Rarefaction – a region of lower-than-normal density

Displacement, y A measure of the disturbance caused by a wave at a certain position and time A wave may disturb any variable property: Position Density Pressure Electric or magnetic field y(x,t)

Crests & Troughs Points of maximum & minimum displacement y

Amplitude, a The maximum displacement of the wave from its natural state y a

Period, T The duration of one wave cycle (in s), or the time between adjacent crests or troughs y T T t

Frequency, f The number of wave cycles per second, measured in Hertz (Hz) Frequency f is the reciprocal of period, T:

Wavelength, λ The length of one full wave (in m), or the distance between adjacent crests or troughs y λ λ x

Wave Speed, v The speed that a wave train propagates through its medium y x

Relating f, λ, and v Recall that speed is defined as Here d = λ and t = T. Hence,

An Example A typical car horn has a frequency of 500 Hz. If the speed of sound is 340 m s-1, what is the distance between compressions when the horn sounds?

Wavefronts Consider a series of adjacent wave trains:

Wavefronts Surfaces through crests and normal to the direction of propagation of the wave

Rays Lines indicating the direction of propagation of a wave (perpendicular to the wavefronts)

Summary Pulse, wave train Compression and rarefaction Displacement, crests & troughs, amplitude Period, frequency, and wavelength Wave speed The wave equation (v = f λ) Applications Wavefronts and rays

Homework In Tsokos: Ch 4.1 - #3, 6, 8, 9, 12, 15, 17, 25, 29, 31, 37