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

2. How Do We Describe Waves?

3. Pulse
A discrete disturbance propagated through a medium

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

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

6. 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)

7. Crests & Troughs
Points of maximum & minimum displacement y

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

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

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

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

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

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

14. 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?

15. Wavefronts
Consider a series of adjacent wave trains:

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

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

18. 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

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