Lesson 1
Announcements
 HW #1 due next Tuesday
 Read pp. 484‐488 (15.1) & p. 494 (15.3)
 Questions: p. 508 (10) p. 509 (21)
 Problems: p. 510 (12,13,17)
AP Physics B Standards
IV.A.1. Traveling waves
Students should understand the description of traveling waves, so they can:
a) Sketch or identify graphs that represent traveling waves and determine the amplitude, wavelength, and frequency of a wave from such a graph.
b) Apply the relation among wavelength, frequency, and velocity for a wave.
d) Describe reflection of a wave from the fixed or free end of a string.
Lesson Objectives
Students will be able to
1.
2.
3.
determine the amplitude, wavelength, period, frequency, and speed of a mechanical wave.
distinguish between transverse and longitudinal waves.
apply Newton’s laws to predict and explain the reflection and refraction of mechanical waves.
Mechanical Wave
A mechanical wave is a disturbance which propagates through a medium with little or no net displacement of the particles of the medium.
Water Waves
Wave “Pulse”
People Wave
http://www.kettering.edu/physics/drussell/Demos/waves/wavemotion.html
Animation courtesy of Dr. Dan Russell, Kettering University
Parts of a Wave
y(m)
3
: wavelength
equilibrium
2
-3
crest
A: amplitude
4
trough
6
x(m)
Wave Speed
 The speed of a wave is the distance traveled by a given point on the wave (such as a crest) in a given interval of time.
v = d/t
 d: distance (m)
 t: time (s)
v = /T or v =  ƒ
 v : speed (m /s)
  : wavelength (m)
 ƒ : frequency (s–1, Hz)
Period and Frequency
f= 1/T
or
 T : period (s)
 ƒ : frequency (s‐1, Hz)
T = 1/ƒ
Sample Problem 1.1
Red light has a wavelength of approximately 700 nm. a) Assuming the light ray is traveling through a vacuum, what is the frequency of the light?
b) What is the period?
c) Violet light has a wavelength of about 400 nm. Does it have a higher or lower frequency than red light?
Wave Types
A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves. Example: Waves on a String
A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves. These are also called compression waves.
Example: sound http://einstein.byu.edu/~masong/HTMstuff/WaveTrans.html
Wave types: transverse
Wave types: longitudinal
Longitudinal vs Transverse
Reflection
• Occurs when a wave strikes a medium boundary and “bounces back” into original medium.
• Completely reflected waves have the same energy and speed as the original wave.
Reflection Types
 Fixed‐end reflection: The wave reflects with inverted phase.  Open‐end reflection: The wave reflects with the same phase
http://www.kettering.edu/physics/drussell/Demos/reflect/reflect.html
Animation courtesy of Dr. Dan Russell, Kettering University
Refraction of waves
• Transmission of wave from one medium to another.
• Refraction is almost always accompanied by some reflection.
• Refracted waves may change speed and wavelength.
• Waves do not change frequency when refracted.
http://www.kettering.edu/physics/drussell/Demos/reflect/reflect.html
Animation courtesy of Dr. Dan Russell, Kettering University
Observations
1.
Compare the speed of the original wave to the reflected and refracted waves.
2. Compare the amplitude (both height and orientation) of the original wave to the reflected and refracted waves.
3. Compare the wavelength of the original wave to the reflected and refracted waves.
4. Use Newton’s laws to explain your observations.
http://www.kettering.edu/physics/drussell/Demos/reflect/reflect.html
Animation courtesy of Dr. Dan Russell, Kettering University
Observations
1.
Compare the speed of the original wave to the reflected and refracted waves.
2. Compare the amplitude (both height and orientation) of the original wave to the reflected and refracted waves.
3. Compare the wavelength of the original wave to the reflected and refracted waves.
4. Use Newton’s laws to explain your observations.
http://www.kettering.edu/physics/drussell/Demos/reflect/reflect.html
Animation courtesy of Dr. Dan Russell, Kettering University