AP Physics B Waves and Energy Transfer TEKS

AP Physics B Waves and Energy Transfer

TEKS Objective: 8 A © 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/string. Wave. 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:

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/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. 4 m)? c) What is the period of the wave?

Homework ©Page 335 #1 -7

$Wave Behavior When waves interact with boundaries they can: ©Reflect ©Refract ©Diffract ©Interfere$

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

$Refraction © Bending of a wave at the boundary between two media as the$

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

$Diffraction ©Waves moving around a barrier. ©Examples: sunset, mirage ©http: //micro. magnet. fsu. edu/primer/java/s$

Diffraction ©Waves moving around a barrier. ©Examples: sunset, mirage ©http: //micro. magnet. fsu. edu/primer/java/s cienceopticsu/diffraction/basicdiffraction

$Diffraction continued:$

Diffraction continued:

Interference ©The superposition of waves, waves pass through each other unchanged, it is only

©Two types: Constructive and Destructive interference

Constructive Interference ©When two waves combine to produce a wave with a larger amplitude,

Destructive Interference ©When two waves combine to produce a wave with a smaller amplitude,

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