Definition of wave: Definition of wave: A periodic disturbance which travels through a medium from...

Definition of wave:Definition of wave:

• A periodic disturbance which travels through a medium from one point in space to the others.

Wave motion means the propagation of waves through a medium.

Wave motion appears in almost every branch of Physics.

• Energy is transferred from one place to another in a wave motion.

• Motion of the medium (particles of the medium) is usually periodically vibratory.

• Only the shape or form of wave travels, not the medium.

Basic properties of wavesBasic properties of waves :

TYPES OF WAVESTYPES OF WAVESWaves Waves are classified into different types according to their natures :

T ra ns ve rs e w a ve s L o ng itud ina l w a ve s

Mechanical w aves

T ra ns ve rs e w a ve s

Elec tromagnetic w aves

WA V E S

Mechanical Waves• A material medium is necessary for the transmission for

mechanical waves. Mechanical waves cannot travel through vacuum.

• Due to elastic forces on adjacent layers of medium, disturbance is transmitted from one layer to the next through the medium.

according to the direction of vibration, waves are also classified into :

(a) Transverse wave;

(b) Longitudinal waves.

And ...

Water waves, sound, vibration of spring, etc.

Transverse WavesTransverse Waves• The waveform appears in the shape of sine curve.

• A wave in which the motions of the matter particles are perpendicular to the direction of propagation of the wave itself.

Water waves, pulse in a stretched string,transverse wave demonstrator.

Longitudinal WavesLongitudinal Waves• A wave in which the motions of the matter particles are in the

same direction as the wave propagation.

Sound, or a spring oscillating up and down, etc.Show magnetic longitudinal demonstrator

Seismic WavesSeismic waves use Earth itself as their medium. Earthquakes produce them and so does a nation when it carries out an underground nuclear test. (Other countries can detect them.) Seismic waves can be longitudinal, transverse, or surface waves. P and S type waves are called body waves, since they are not confined to the surface. Rayleigh waves do most of the shaking during a quake.

Name Type Info

P Wave LongitudinalAlso known as primary, compressional, or acoustic waves; fastest seismic wave

S wave TransverseAlso known as secondary, or shear

waves do not travel through fluids;

Rayleigh Wave

SurfaceRolls along surface like a water wave;

large amplitude

Love Wave SurfaceGround moves side to side

as wave moves forward

Seismic WavesSeismic WavesVibrations passing through the ground that result from an earthquake

The seism focus generates spherical pulses

or primary (P) waves, which propagate like

concentric waves.

P waves have a longitudinal action; they cause change

in volume (compression and dilatation of the ground)

- Their velocity is high: 5 – 8 km/s.

S (secondary) waves, induced by P waves, are transversal waves (soil oscillates perpendicular to direction) - They are very destructive. - Their velocity is around 3 – 5 km/s

Terminology of a Wave

• Amplitude • Wavelength ()• Frequency (f)• Period (T)• Wave velocity (v)

A wave is usually described by the following terms :

Each term will be explained….

• The amplitude is the maximum displacement of the medium from its equilibrium position.

• The wavelength () is the minimum distance between two points which are in phase.

• The frequency (ƒ) is the number of complete oscillations made in one second. Unit : Hz

• The period (T) is the time taken for one complete oscillation. It is related to frequency by T = 1/ƒ Unit : s

Frequency and Period are related

T = 1/f

F= 1/T

The Wave EquationThe Wave Equation

The wave velocity is the displacement traveled by the wave in one second ……....

The wave velocity (v) is related to frequency and wavelength by --

v = ƒv = ƒThe Wave Equation

Using the Wave EquationUsing the Wave EquationExample :

A traveling wave of wavelength 0.6m moves at a speed of 3.0 m/s. What is the period of this wave ?

Then the period of this wave is ???Period T = 1/ƒ T = 1/5.0 or 0.2 s

Now you know = 0.6 m, v = 3.0 m/s Can you find the frequency of this wave……

Table ofContents

By using the wave

equation, v = ƒ 3.0 = ƒ(0.6) i.e ƒ = 5.0 Hz

Practice problems 12 D page 457

Work problems 1-4

• Transmission of Transmission of energyenergy

• ReflectionReflection• RefractionRefraction• DiffractionDiffraction• InterferenceInterference

Let’s take water waves as an example to study the characteristics of waves….

The behavior of water waves demonstrates all these characteristics……..

Reflection (bounce)

Reflection

Reflection of WavesReflection of Waves

A traveling wave is reflectedreflected when it hits a barrier.

This phenomenon can easily be observed when a traveling waterwave hits a reflector in the ripple tank.

Reflection of WavesReflection of Waves

Reflectedwaves

Reflectedwaves

Reflector

ReflectionThe law of reflection: the angle of incidence equals the angle of reflection

NOTE: Angles in opticsare taken from the normalline to the surface

Refraction (bending of waves)

Refraction of WavesRefraction of Waves

- The speed of a water wave increases with depth. This change in speed is accompanied by refraction refraction.

This effect is a consequence of the wave equation, v = ƒ.Since ƒ is constant, a decrease in v produces a decrease in .

Diffraction of WavesDiffraction of Waves

When a traveling water wave hits an obstacle, the wavefronts spreads out round the edge and becomes curved. This phenomenon refers to diffraction..

The wavelength of the wave is not changed in diffraction.

Diffraction

Small openings cause diffraction, even curved waves will diffract

Two openings will allow diffracted waves to interfere with

each other.

Interference• when two waves are combined, either

constructive or destructive interference can occur.

constructiveinterference

destructiveinterference

Constructive Interference

Destructive Interference

Polarization

• a transverse wave is linearly polarized with its vibrations always along one direction

• a linearly polarized wave can pass through a slit that is parallel to the vibration direction

• the wave cannot pass through a slit that is perpendicular to the vibration direction

Polarizing sunglasses

Polarization

is known as

ACOUSTICS

Properties of SoundProperties of Sound

• A sound is a vibration• The vibrating causes the air molecules near the

movement to be forced closer. This is called compression

• As the vibration moves on, the density and air pressure becomes lower than normal and is called rarefaction

• Pressure wave – longitudinal• Frequency = pitch• v = 334 m/s in air at room temperature• Velocity is dependent upon the material

Guitar String creating a sound wave

Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com

Do molecules move faster or slower Do molecules move faster or slower as temperature increases?as temperature increases?

So would sound travel faster or slower as So would sound travel faster or slower as temperature increases?temperature increases?

Can affect speed

•requires a medium

(cannot travel in a vacuum)

Waves travel fastest in solids, slowest in gases.Waves travel fastest in solids, slowest in gases.

SolidSolid LiquidLiquidGasGas

•Fastest in solids, slowest in gases.

Air = 340 m/swater= 1440 m/ssteel = 5000 m/s

•Supersonic: faster than the speed of sound.

http://www.youtube.com/watch?v=-d9A2oq1N38&feature=related

•Sound travels faster in warm water than in cold water

•By measuring the time it takes for sound to travel a known distance through the ocean the average temperature of the water can be calculated = ATOC (acoustic thermometry of ocean climate)

Speeds of SoundSpeeds of Soundat Temp = 20at Temp = 2000 C C

• Air Air • HeliumHelium• HydrogenHydrogen• WaterWater• Sea waterSea water• Iron/SteelIron/Steel• GlassGlass• AluminumAluminum

• 343 m/s

• 1005 m/s

• 1300 m/s

• 1440 m/s

• 1560 m/s

• ≈5000 m/s

• ≈ 4500 m/s

• ≈ 5100 m/s

The highness or lowness of sound.

Depends on the frequency of sound waves.

High frequency = High pitch

Low frequency = Low pitch

•Also called LOUDNESS•Amount of energy•Depends on the amplitude of sound waves. (amplifier)

Large Amp. = Loud sound

Small Amp. = Soft sound

Intensity of SoundIntensity of Sound

• Unit is the “Bel”. Named after Alexander Unit is the “Bel”. Named after Alexander Graham Bell Graham Bell

• More commonly used is the decibel (dB)More commonly used is the decibel (dB)

Some Intensities (in dB)Some Intensities (in dB)

• Jet plane at 30 mJet plane at 30 m• Threshold of painThreshold of pain• Indoor rock concertIndoor rock concert• Auto interior Auto interior • Street trafficStreet traffic• Conversation Conversation • WhisperWhisper• Rustle of leavesRustle of leaves

• 140

• 120

• 120

• 75

• 70

• 651

• 45

• 20

•Sound waves reflecting from hard surfaces•Ex.: Multiple echo resulting from the direct sound AND the reflected sound

Reverberation vs Echo

Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com

Near total silence - 0 dB

A whisper - 15 dB

Normal conversation - 60 dB

Lawnmower - 90 dB

Threshold of pain - 120 dB

A rock concert or a jet engine - 120 dB

Gunshot, firecracker - 140 dB

Measurement of loudness

Sound is a pressure wave

Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com

Resonance

Forced vibrations

Something makes something else vibrate that has the same natural frequency.

Examples of Resonance

• Tuning forks

• Resonance boxes

• Tacoma Narrows Bridge

• Wine glasses

• Shattering a wine glass http://www.youtube.com/watch?v=Jy8js2FmGiY

http://www.youtube.com/watch?v=hiHOqMOJTH4

Ear

Range of Human Hearing

20Hz through 20,000Hz typical people can hear these frequencies

Above or below, we can’t hear.

Infrasonic – too low to hear

Ultrasonic – too high to hear

http://www.freemosquitoringtones.org/hearing_test/

Mosquito ringtones, do they work?

Tuning fork creating a sound wave

Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com

UltrasoundsUltrasounds

• Ultrasound can be used to create internal images of the human bodyx. Pregnant woman gets a “picture” of her unborn baby

Ultrasound of 13 week old

http://www.youtube.com/watch?v=TW6aMRUqeZU&feature=related

Used to locate underwater objects and distances.

How deep is the water in this picture? Speed of sound

in water is 1400m/s. Time from emitted sound until

detected is 1.5seconds.

Echolocation

Doppler EffectDoppler Effect

• Apparent change in frequency (pitch) of a Apparent change in frequency (pitch) of a sound from a moving source.sound from a moving source.

Change in pitch due to motion.Change in pitch due to motion.

http://www.youtube.com/watch?v=O5rqMPdQMQ8

*Moving *Moving towards towards increasesincreases the the pitchpitch

*Moving *Moving awayaway decreases the pitch decreases the pitch

*Think of sirens*Think of sirens

Doppler Radar

Electromagnetic Waves

All travel at the same speed in the same medium.Fastest in a vaccuum, slower in

air, slower under water, …

All are produced by a vibrating Charge (usually an electron)

Wave Particle Duality of Light

Light is a wave (it diffracts, interferes, and refracts)

Light is a particle (it is affected by gravity and travels in a vacuum) (it behaves like it has mass but it doesn’t)

A photon is a tiny package of energy and the way to conceptualize light.

Light is both a wave and a particle

Electromagnetic Waves• Material medium is not essential for propagation. e/m

waves travel through vacuum.

• Disturbance of electric and magnetic fields traveling through space.

• All electromagnetic waves are transverse waves.

X-rays, radio waves, micro-waves,etc.

Electromagnetic WavesElectromagnetic Waves Energy produced by the oscillation of an electric charge which produces electric and magnetic fields

(spectrum is any range of wavelengths or frequencies)

X-RaysX-Rays- Discovered by accident in 1895 by German scientist Wilhelm Conrad Roentgen while experimenting with vacuum tubes

A week later he took this x-ray of his wife

The Earth's atmosphere is thick enough that virtually no X-rays are able to penetrate from outer space all the way to the Earth's surface

Many things in space emit X-rays: black holes, neutron stars, binary star

systems, supernova remnants, stars, the Sun, and even some comets! Supernova remnants in

the Small Magellanic Cloud

C = the speed of light (and all EM waves)

3.0 x 108 m/s186,000 miles/sec

Nature of Electromagnetic WavesThey are Transverse waves without a medium. (They

can travel through empty space)They travel as vibrations in electrical and magnetic

fields.Have some magnetic and some electrical properties to

them.

Speed of electromagnetic waves = 300,000,000 meters/second (Takes light 8.3 minutes to move from the sun to earth {93 million miles} at this speed.

When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.

RESULT-An electromagnetic wave.

Waves or Particles

Electromagnetic radiation has properties of waves but also can be thought of as a stream of particles.

Example: Light

Light as a wave: Light behaves as a transverse wave which we can filter using polarized lenses.

Light as particles (photons)

When directed at a substance light can knock electrons off of a substance (Photoelectric effect)

B. Waves of the Electromagnetic SpectrumElectromagnetic Spectrum—name for the range of electromagnetic

waves when placed in order of increasing frequency

RADIO WAVES

MICROWAVES

INFRARED RAYS

VISIBLE LIGHT

ULTRAVIOLET RAYS

X-RAYS

GAMMA RAYS

RADIO WAVESA. Have the longest wavelengths and lowest frequencies

of all the electromagnetic waves.

B. A radio picks up radio waves through an antenna and converts it to sound waves.

C. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.

D. MRI (MAGNETIC RESONACE IMAGING)Uses Short wave radio waves with a magnet to create an image

MRI

AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.

(535kHz-1605kHz= vibrate at 535 thousand to 1.605 million times/second)

+

FM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range.

(88MHz-108MHz = vibrate at 88million to 108million times/second)

+

Bands of Radio/TV/Microwaves

MICROWAVESUsed in microwave ovens.

Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.

Used by cell phones and pagers.

RADAR (Radio Detection and Ranging)Used to find the speed of an object by sending out

radio waves and measuring the time it takes them to return.

INFRARED RAYSInfrared= below red

Shorter wavelength and higher frequency than microwaves.

You can feel the longest ones as warmth on your skin

Heat lamps give off infrared waves.

Warm objects give off more heat energy than cool objects.

Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.

VISIBLE LIGHTShorter wavelength and higher frequency than

infrared rays.Electromagnetic waves we can see.Longest wavelength= red lightShortest wavelength= violet (purple) lightWhen light enters a new medium it bends (refracts).

Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.

ULTRAVIOLET RAYSShorter wavelength and higher frequency than

visible lightCarry more energy than visible lightUsed to kill bacteria. (Sterilization of equipment)Causes your skin to produce vitamin D (good for

teeth and bones)Used to treat jaundice ( in some new born babies.Too much can cause skin cancer. Use sun block to protect against (UV rays)

X- RAYS

Shorter wavelength and higher frequency than UV-raysCarry a great amount of energyCan penetrate most matter.Bones and teeth absorb x-rays. (The light part of an x-ray

image indicates a place where the x-ray was absorbed)Too much exposure can cause cancer

(lead vest at dentist protects organs from unnecessary exposure)

Used by engineers to check for tiny cracks in structures.The rays pass through the cracks and the cracks appear dark on

film.

GAMMA RAYS

Shorter wavelength and higher frequency than X-rays

Carry the greatest amount of energy and penetrate the most.

Used in radiation treatment to kill cancer cells.

Can be very harmful if not used correctly.

Test ReviewSuperposition is constructive and destructive interference. Look at the wave, find the amplitudes at all 4 points.

Find angle of incidence

What is about to happen?

What is about to happen?

What causes this?Why does it happen?

What is going on here?