Title: Physics 211 lecture 26: Wave Motion
1Physics 211 lecture 26 Wave Motion
- Waves consist of disturbances that propagate
through a substance or region of space. - Waves typically consist of either a single
disturbance (wave pulse) or a series of
disturbances one after another (periodic wave). - Two types of waves
- Mechanical - travel through
matter -
observed as a disturbance in matter - Examples earthquakes,
sound, water waves, strings, slinky, - Electromagnetic - travel through
matter or empty space
- observed as a disturbance in
electric and magnetic fields - Examples radio, TV,
X-ray, gamma ray, microwave, all other EM waves -
- Two ways waves propagate
- Longitudinal Waves - disturbances
move parallel to direction of wave - Examples sound, lines at
stadiums, - Transverse Waves - disturbances move
perpendicular to direction of wave - Examples EM waves, water
waves (mostly), stadium wave cheer,
2Wave Properties
- wavelength ( ? ) - length between
two similar points on a wave - angular wave number ( k ) - amount of wave
angle fitting in a unit of distance - period ( T ) - time for one full
wavelength to pass by a fixed point - frequency ( f ) - number of
wavelengths passing by per unit of time - angular frequency ( ? ) - amount of wave
angle passing by per unit of time - amplitude ( A )- maximum movement
from disturbance by wave
Diagram Team task Draw a wave and label as
many properties as you can
Wave Equations
3Example (Waves) Find wavelength for X-ray with
f1018Hz in tissue and in air.
Given Path
Want Conversions/Equations
Example (Waves) Find speed of ocean wave w/
period 15s and wavelength 25m.
Given Path
Want Conversions/Equations
4Wave Behavior at an Interface
- Reflection portion of wave changes direction to
avoid entering a new medium at an interface - Inverted wave rebounds with same displacement
as arrival - Non-inverted wave rebounds with negative
displacement of arrival - Transmission portion of wave continues at
reduced energy into a new medium through an
interface - Diagrams Team task draw and label
- 1) an inverted reflection 2) a non-inverted
reflection 3) transmission
5Wave Equations
- The wave function assume wave travels in
x-direction as a function of time
Displacement of wave with time due to wave
propagation
Height of wave above or below equilibrium
Position at which you observe the wave
The sinusoidal wave function
Diagram
Substitute in to write in terms of angular wave
number and angular frequency
To see how the wave moves visit http//www.silcom
.com/aludwig/images/snake.gif
Note if timing of wave does not start at y0,
then must add in phase constant ? to sine term
6- Example Ch 16 2
- Ocean waves with crest-to-crest distance of 10m
can be described by the wave function y(x,t)
(0.8m) sin0.628(x - vt) where v1.2m/s. - Sketch y(x,t) at t0s
- Sketch y(x,t) at t2s
- How far did the wave shift during this time?
7- Example Ch 16 13
- A sinusoidal waves is described by
- y (0.25m) sin(0.3x 40t) with x,y in meters
and t in seconds. Find the - amplitude
- angular frequency
- angular wave number
- wavelength
- wave speed
- direction of motion
8Questions for Groups
- 16.6 If you shake one end of a taut rope
steadily three times per second, what would the
period of the sinusoidal wave set up in the rope? - 16.16 Earthquakes create both S (longitudinal at
about 5km/s) and P (transverse at about 8km/s)
waves that emanate from the focus. By detecting
the arrival time of the waves, how can one
determine the distance to the focus? Also, how
many stations are needed to locate the focus
unambiguously?