Waves and Energy Transfer 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/simulations/stringwave/stringWave.swf A repeated disturbance is a continuous wave pattern

Wave properties 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:

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

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/waves/lw.html

Example Problem A sound wave has a frequency of 262 Hz and a wavelength of 1.29 m. What is the speed of the wave? How long will it take the wave to travel the length of a football field (91.4m)? 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

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, mirage http://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 motion Antinode 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 #8-10 Review problems page 346 #32-47