1

Physics 120 1

Wave Motion

Physics 120 2

Wave Motion

Physics 120 3

Wave Characteristics

Physics 120 4

Velocity of Waves

For all waves:

For a wave on a string or cord (stringinstruments):

2

Physics 120 5

Ch 11: Problem 38

(a) AM radio signals have frequenciesbetween 550 kHz and 1600 kHz and travelwith a speed of 3.00 x 108 m/s. What are thewavelengths of these signals?

(b) On FM, the frequencies range from 88.0MHz to 108 MHz and travel at the samespeed. What are their wavelengths?

Physics 120 6

Types of waves (11-8)

Transverse displacement is

perpendicular to velocity Ex - light

Longitudinal displacement is parallel

to velocity Ex - sound

Physics 120 7

Energy Transport in Waves (11-9)

Energy is proportional to A2

Intensity, I

Physics 120 8

Reflection & Transmission (11-11)

3

Physics 120 9

Reflection & Transmission

Physics 120 10

Wave Fronts & Rays

Wave fronts connects peaks

Ray perpendicular to wave

front shows direction of motion

Physics 120 11

Reflection of plane waves

Law of reflection: angle of incidence = angle of reflection angle measured from normal

Physics 120 12

Interference;Principle of Superposition (11-12)

DestructiveInterference

ConstructiveInterference

PartialDestructiveInterference

4

Physics 120 13

Standing Waves; Resonance (11-13)

wheren = 1,2,3,...

Physics 120 14

Ch 11: Problem 52

If a violin string vibrates at 440 Hz as itsfundamental frequency, what are thefrequencies of the first four harmonics?

Physics 120 15

Refraction (11-14)

Physics 120 16

Diffraction (11-15)

When waves encounter an obstacle, theybend around it somewhat.

Amount ofdiffraction

wavelength ofwave

size of openingor obstacle

5

Physics 120 17

Think-Pair-Share

Ch 11: Problem 72 When you walk with a cup of coffee (diameter 8

cm) at just the right pace of about 1 step persecond, the coffee sloshes more and more untileventually it starts to spill over the top. Estimatethe speed of the waves in coffee.