Waves

Properties of WavesProperties of Waves

May 4, 2014May 4, 2014

ObjectivesObjectives

1.1. Recognize the different types of wavesRecognize the different types of waves

2.2. Sketch and identify the different parts of Sketch and identify the different parts of a transverse wavea transverse wave

3.3. Define and calculate the properties of Define and calculate the properties of waveswaves

WavesWaves

Not just the ones you surf on!!!!Not just the ones you surf on!!!!

A vibration that moves through space and A vibration that moves through space and timetime Light and soundLight and sound

Types of WavesTypes of Waves

1.1. Transverse wavesTransverse waves

2.2. Longitudinal or Compressional waves - Longitudinal or Compressional waves - soundsound

3.3. Electromagnetic waves – lightElectromagnetic waves – light

Common pointsCommon points Crests and TroughsCrests and Troughs Midpoints – horizontal line between the Midpoints – horizontal line between the

crests and troughscrests and troughs

Amplitude – distance from the midpoint to Amplitude – distance from the midpoint to the crest or trough the crest or trough

Wavelength – distance from one crest to Wavelength – distance from one crest to the next (any consecutive point)the next (any consecutive point)

Wave train – two or more waves in a row

0 x

Frequency – the number of vibrations the Frequency – the number of vibrations the object makes during a certain time interval object makes during a certain time interval (s)(s) F = Cycles/SecondsF = Cycles/Seconds Measured in Hertz (Hz)Measured in Hertz (Hz)

Period – time it takes for a complete Period – time it takes for a complete vibrationvibration Period = Seconds/CyclesPeriod = Seconds/Cycles Period and Frequency are relatedPeriod and Frequency are related

Frequency = 1/Period Period = 1/Frequency Frequency = 1/Period Period = 1/Frequency

ExamplesExamples

1.1. An electric toothbrush completes 90 An electric toothbrush completes 90 cycles every second. What is it’s cycles every second. What is it’s frequency? What is its period?frequency? What is its period?

2.2. Gusts of wind cause the Sears building Gusts of wind cause the Sears building in Chicago to sway back and forth, in Chicago to sway back and forth, completing a cycle every ten seconds. completing a cycle every ten seconds. What is its frequency? What is its What is its frequency? What is its period?period?

Problem

A weight suspended from a spring bobs up and down over a distance of 20 cm twice each second. What is its frequency? Its period? Its amplitude?

Waves transport energyWaves transport energy

How much energy depends on wave How much energy depends on wave speedspeed

Wave speed = frequency x wavelengthWave speed = frequency x wavelength

ExamplesExamples

1.1. If a train of freight cars, each 10m long, If a train of freight cars, each 10m long, rolls by you at the rate of three cars each rolls by you at the rate of three cars each second, what is the speed of the train?second, what is the speed of the train?

2.2. If a water wave vibrates up and down If a water wave vibrates up and down three times each second and the three times each second and the distance between the wave crests is 2m, distance between the wave crests is 2m, what is the wave’s frequency? Its what is the wave’s frequency? Its wavelength? Its wave speed?wavelength? Its wave speed?

Problem

A skipper of a boat notices wave crests passing his anchor chain every 5s. He estimates the distance between wave crests to be 15 m. He also correctly estimates the speed of the waves. What is this speed?

Frequency and Wave Speed

May 13, 2011