AP Physics
Waves and Energy Transfer
TEKS Objective: 8A
The student knows the characteristics and
behavior of waves. The student is expected to:
(A) Examine and describe waves propagated in
various types of media and describe wave
characteristics such as velocity, frequency,
amplitude, and behaviors such as reflection,
refraction, and interference.
Two Main Topics
Wave properties
Wave behavior
Waves transfer energy
A wave pulse is a single disturbance
http://www.colorado.edu/physics/phet/si
mulations/stringwave/stringWave.swf
A repeated disturbance is a continuous
wave pattern
Wave properties
1. Mechanical Waves – transfer energy,
require a medium and obey Newton’s
Laws of Motion
What is a medium?
 Sound waves – called compressional or
longitudinal waves
 Transverse wave – move through the
medium, making an “s” shape
2. Measuring Waves
 Speed – how fast the
wave is moving
 Unit: m/s
Formula:
vf
2. Measuring waves continued:
Amplitude – maximum displacement from
equilibrium
Wavelength – the distance need to make
one complete cycle or wave, usually
measured from crest to crest (λ), usually
measured in meters.
2. Measuring waves continued:
Period – the time needed to make one
complete wave or cycle
(T) unit is usually the second
Frequency – the number of waves or
cycles in a time unit (usually one second)
(f) Unit is the Hertz (Hz)
2. Measuring Waves
continued:
Period and frequency have an inverse
relationship
1
f 
T
1
T
f
3. Parts of a Wave
Crest – highest point of a wave
Trough – lowest point of a wave
Amplitude – maximum displacement from
line of equilibrium
Wavelength – λ the distance needed to
complete one wave or cycle
Parts of a Transverse Wave
4. Two types of waves:
Transverse – particles vibrate
perpendicular to the direction of the wave
motion
Longitudinal or compressional –
particles vibrate parallel to the direction
the wave motion. Examples: sound
waves, primary earthquake waves
http://physicsclassroom.com/mmedia/wav
es/lw.html
Example Problem
A sound wave has a frequency of 262 Hz
and a wavelength of 1.29 m.
a) What is the speed of the wave?
b) How long will it take the wave to travel
the length of a football field (91.4m)?
c) What is the period of the wave?
Homework
Page 335 #1-7
Wave Behavior
When waves interact with boundaries they
can:
Reflect
Refract
Diffract
Interfere
Reflection
Is when a wave bounces back off a
boundary or barrier
Parts of Reflection
Normal – the imaginary line
perpendicular to the barrier at the point
of reflection
Angle of incidence – angle between the
incident ray and the normal
Angle of reflection – angle between the
normal and the reflected ray
Parts of reflection continued:
Law of Reflection – for a smooth surface,
the angle of incidence equal the angle of
reflection
i   r
Refraction
 Bending of a wave at the boundary between two media
as the wave moves from one medium to another,
velocity and wavelength change, but period and
frequency remain constant
http://physicsclassroom.com/mmedia/opti
cs/bp.html
Diffraction
Waves moving around a barrier.
Examples: sunset, mirage
http://micro.magnet.fsu.edu/primer/java/s
cienceopticsu/diffraction/basicdiffraction
Diffraction continued:
Interference
The superposition of waves, waves pass
through each other unchanged, it is only
a displacement of matter
Two types: Constructive and Destructive
interference
Constructive Interference
When two waves combine to produce a
wave with a larger amplitude, the meet
crest to crest
Destructive Interference
When two waves combine to produce a
wave with a smaller amplitude, they meet
crest to trough
Total destructive interference
Standing Waves
When two waves meet with equal and
opposite amplitudes
Parts of a standing wave: node and
antinode
Node is the area of no apparent motion
Antinode is the area of maximum
displacement
http://physicsclassroom.com/Class/waves
/U10L4b.html
http://www.colorado.edu/physics/phet/si
mulations/stringwave/stringWave.swf
Homework
Page 337 #8-10
Review problems page 346 #32-47