Chapter 11 Waves and Wave properties. What is a wave? A wave is a disturbance that carries energy...
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Transcript of Chapter 11 Waves and Wave properties. What is a wave? A wave is a disturbance that carries energy...
Chapter 11Waves and Wave
properties
What is a wave?
A wave is a disturbance that carries energy through matter or space
Waves
Waves that require a medium are called mechanical wavesElectromagnetic waves, also called light waves, are the only waves that do not require a medium
Electromagnetic Waves
Light waves consist of changing electric and magnetic fields in spaceExamples: UV, infrared, and visible light waves
Waves and energy
We know that waves carry energy because they can do workThe bigger a wave is, the more energy it carriesA tsunami is a huge ocean wave, that can carry enough energy to cause extensive damage to coastal towns and shorelines
Energy and Waves
Energy spreads out as a wave travelsWaves are related to vibrationsMost waves are caused by a vibrating objectVibrations involve transformations of energy
Transverse and Longitudinal
Particles in a wave can either move up and down OR back and forthWaves are classified by the direction the particles moveTransverse wave Longitudinal wave
When a crowd does “the wave” at a sporting event, they are performing as a transverse waveThe wave moves in a circle around the stadium, but the people move up and downThe motion of the particles in the medium is at a right angle to the motion of the wave as a whole
Transverse Waves
Longitudinal Waves
A longitudinal wave causes the particles of the medium to vibrate parallel to the direction the wave travelsExample: Sound waves
Longitudinal Waves
A longitudinal wave can be created by a slinky when the first coils of the slinky are vibrated horizontally.
Surface Waves
Some waves are not longitudinal waves OR transverse wavesThese other waves are surface wavesWater waves are surface wavesSurface waves occur at the boundary between two different mediums, like the boundary between water and air
Characteristics of Waves
All transverse waves, no matter their size or what medium they are traveling though, have similar shapesAn ideal transverse wave has the shape of a sine curve
Amplitude in Transverse Waves
Amplitude measures the amount of particle vibrationThe highest points on a transverse wave are called the crestsThe lowest parts on a transverse wave are called the troughsThe greatest distance that particles in a normal medium move from their normal position when a wave passes is called the waves amplitude
Amplitude in longitudinal waves
Longitudinal waves do not have crests and troughs because the particles do not move up and downA longitudinal wave has compressions and rarefactions insteadThe high and low points of a sine wave correspond with the compressions and rarefactions of a longitudinal wave
Comparing Waves
Wavelength
The distance between any two successive identical parts of a wave is called its wavelengthSo, in a transverse wave, the distance from the crest of a wave to the crest of the next wave, or the distance from the trough of one wave to the trough of another is an example of one wavelength
Wavelength
In a longitudinal wave, the distance between two compressions or two rarefactions is one wavelengthWhen used in equations, wavelength is represented by the Greek letter lambda,Because lambda is an SI unit, we label it in meters
Frequency
The frequency of a wave is the number of full wavelengths that pass in a given time interval, its symbol is f and its units are HertzIt measures how rapidly vibrations occur in a medium
Hertz
Hertz units measure the number of vibrations per secondThe SI unit Hertz is named after Heinrich Hertz, who in 1888, demonstrated that electromagnetic waves exist
LightLight comes in a wide range of frequencies and wavelengthsOur eyes can detect light with frequencies ranging from 4.3 x 1014 Hz to 7.5 x 1014 HzLight in this range is called visible light
Wave Speed EquationWave speed equals frequency times wavelengthWave speed is represented with a V and is measured in m/sFrequency is represented by a f and is measured in HertzWavelength is represented by lambda and is measured in meters
V
f Wavelength, labeled in meters
Frequency, labeled in HZ
Wave Speed, labeled in m/s
Characteristics of waves
The speed of a wave depends on the medium it is traveling throughIn a given medium however, the speed of a wave is constantAll electromagnetic waves in empty space travel at the same speedThat speed is 3.0 x 108 m/sThe speed of light is represented by the symbol c
Wave Interactions--Reflection
Reflection is what happens when a wave strikes a surface or boundaryWaves reflect at a free boundaryAt a fixed boundary, waves reflect and turn upside down
Wave Interactions--Diffraction
When waves pass the edge of an object or pass through an opening, such as a door, they are being bentThis bending of waves around an edge is called diffractionThe bending due to diffraction is not smooth it is abrupt and sudden, like changing directions while running down the hall
Wave Interactions--Refraction
When waves pass from one medium into another, they are bending due to a process called refractionThis is why a spoon looks like it is broken into 2 pieces when it is resting in a glass half-full of water
Interference
The combination of two or more waves that exist in the same place at the same time is called interference
Interference
In constructive interference, amplitudes are added
red = first wave blue = second wave green = resulting wave
Interference
In destructive interference, amplitudes are subtracted
red = first wave blue = second wave green= resulting wave
Standing Waves
A standing wave is a form of a waveStanding waves DO NOT move through a medium
Areas of no vibration are called nodesMidway between the nodes are points of maximum vibration.Areas of maximum vibration are called antinodes
Nodes and Antinodes
THE END