ap physics waves and energy transfer. teks objective: 8a the student knows the characteristics and...
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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 propertiesWave behavior
Waves transfer energyA wave pulse is a single disturbancehttp://www.colorado.edu/physics/phet/
simulations/stringwave/stringWave.swfA 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 secondFrequency – 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
1
fT
Tf
3. Parts of a Wave
Crest – highest point of a waveTrough – lowest point of a waveAmplitude – maximum displacement from
line of equilibriumWavelength – 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/waves/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:
ReflectRefractDiffractInterfere
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/optics/bp.html
Diffraction
Waves moving around a barrier.Examples: sunset, miragehttp://micro.magnet.fsu.edu/primer/java/
scienceopticsu/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 motionAntinode is the area of maximum
displacement
http://physicsclassroom.com/Class/waves/U10L4b.html
http://www.colorado.edu/physics/phet/simulations/stringwave/stringWave.swf
Homework
Page 337 #8-10Review problems page 346 #32-47