Oscillations Waves Lesson 4 C Basic Wave Concepts

Oscillations & Waves Lesson 4 C 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 – Ch 4. 2 - #1, 3, 6, 7, 12, 15, 17 – Ch 4. 3 - #1, 4, 5, 7, 10 – Ch 4. 4 - #1, 4, 7