Vocabulary you’ll need …

Read in the textbook Chapter 25- Vibrations and WavesRead in the textbook Chapter 25- Vibrations and Waves

pendulum wave appletvibrating spring wave

applet

Wave Wave a a disturbancedisturbance that that propagates through a propagates through a material material mediummedium or or spacespace..

Waves Waves transfer energytransfer energy without the bulk transport of without the bulk transport of matter.matter.

Types of WavesTypes of Waves

Waves are classified byWaves are classified by

1) The 1) The use of a mediumuse of a medium or or not to carry the energy not to carry the energy

2) The 2) The way they vibrateway they vibrate relative to the motion of the relative to the motion of the wavewave

Mechanical WavesMechanical Waves In order for a In order for a mechanical wavemechanical wave to exist, to exist, energyenergy is needed to is needed to create a create a disturbancedisturbance in an in an elastic mediumelastic medium..

Light, radio, x-rays, and gamma Light, radio, x-rays, and gamma rays are some examples of e/m rays are some examples of e/m waves.waves.

No medium is needed forNo medium is needed forELECTROMAGNETICELECTROMAGNETIC waves waves..

Electromagnetic WavesElectromagnetic Waves

.

                                                                              

All e/m wavesAll e/m waves travel travel through free space at a through free space at a speed of approximatelyspeed of approximately

3.00 x 103.00 x 1088 m/s or 186,000 m/s or 186,000 miles/sec.miles/sec.

This speed is known as This speed is known as the speed of light the speed of light cc..

ELECTROMAGNETIC ELECTROMAGNETIC WAVESWAVES

The displacement of the The displacement of the particles of the medium is particles of the medium is perpendicularperpendicular to the direction to the direction of wave propagation.of wave propagation.

TRANSVERSETRANSVERSE

                                                                                                 

                                                

Parts of a transverse waveParts of a transverse wave

Demo slinky Demo slinky wavewave

LONGITUDINAL

LONGITUDINAL

The displacement of the particles The displacement of the particles of the medium is of the medium is parallelparallel to the to the direction of wave propagation.direction of wave propagation.

Slinky demo…Slinky demo…

WavelengthWavelengththe the shortest distanceshortest distance

betweenbetweentwo points that are “in two points that are “in

phase”phase”denoted by denoted by and measured in units of length and measured in units of length

AmplitudeAmplitudethe the maximum displacementmaximum displacement

of a particle of the medium fromof a particle of the medium fromthe rest or equilibrium positionthe rest or equilibrium positiondenoted by A and measured in units of lengthdenoted by A and measured in units of length

frequencyfrequency - - the number of complete the number of complete vibrations per unit timevibrations per unit time

denoted by f and measured in units of Hzdenoted by f and measured in units of Hz

periodperiod - - the shortest the shortest timetime interval during interval duringwhich the motion of the wave repeats itselfwhich the motion of the wave repeats itself

denoted by T and measured in units of timedenoted by T and measured in units of time

T = 1/f

& f = 1/T

velocityvelocity - the - the speedspeed of the wave of the wave

denoted by v and measured in units of dist/timedenoted by v and measured in units of dist/time

v = d/t = /T = f

The speed of a wave depends on the propertiesThe speed of a wave depends on the propertiesof the medium through which it is traveling.of the medium through which it is traveling.

Example: Measurements show that the wavelength of a sound wave in a certain material is 18.0 cm. The frequency of the wave is 1900 Hz. What is the speed of the sound wave?

λ = 0.18 mf = 1900 Hz

v = λ f = 0.18 (1900) = 342 m/s

ReflectionReflectionthe the turning backturning back of a wave whenof a wave whenit reaches the it reaches the boundaryboundary of the of themedium through medium through which it is which it is travelingtraveling

Reflection of WavesReflection of WavesReflection from Reflection from a hard a hard boundary or boundary or fixed-end fixed-end

Reflection from Reflection from a soft a soft boundary or boundary or free-end free-end

The wave is The wave is invertedinverted,,or flipped or is or flipped or is a 180º out of phase a 180º out of phase

The wave is reflected The wave is reflected right side up or right side up or remains remains the samethe same, or remains in , or remains in phasephase

Law of ReflectionLaw of Reflection

the the angle of incidenceangle of incidence is is equalequalto the to the angle of reflectionangle of reflection

Sound can also be reflectedSound can also be reflected

Reflected sounds are Reflected sounds are EchoesEchoes

the bendingbending of a wave as it passes obliquelyobliquely from one medium into another of different propagation different propagation

speedspeed

RefractionRefraction

For refraction to occur, For refraction to occur,

the wave mustthe wave must change speedchange speed

and must enter the and must enter the new medium at an new medium at an oblique angleoblique angle..

Refraction occurs Refraction occurs because wave because wave speed speed changeschanges in in different materialsdifferent materials

In medium 2, the wave travels In medium 2, the wave travels slower than in medium 1. This slower than in medium 1. This change in speed causes a bending change in speed causes a bending toward the normal of the wave. This toward the normal of the wave. This behavior is important in lensesbehavior is important in lenses

DiffractionDiffractionthethe spreadingspreading of a of a

wavewavearound a barrier oraround a barrier orthrough an openingthrough an opening

In order for diffraction to In order for diffraction to occur, the opening or edge occur, the opening or edge must be much smaller than must be much smaller than the incident wave the incident wave

These These images are images are created by a created by a ripple tankripple tank

InterferenceInterference

the result of thethe result of the superposition superposition of two or more wavesof two or more waves

Superposition Principle Superposition Principlethe displacement of the medium when the displacement of the medium when two or more waves pass through it at the two or more waves pass through it at the same time is the same time is the algebraic sumalgebraic sum of the of the displacements causeddisplacements causedby the individual wavesby the individual wavesThese two wave pulses are moving towards each other. What will happen when they are on top of each other?

Notice that wave A has an amplitude of 2, while wave B has an amplitude of 1.Both of the wave pulses are erect, so we say that they have positive values As they come together in the middle, both of them are pulling upwards…

NOTE: They are still two separate waves, they just happen to be in the same spot at the same time.

They will continue moving on and look exactly the way they looked before they hit each other.

This is an example of Constructive Interference.

When they are directly over each other, they are both shoving particles up together, so the two waves become one big wave with an amplitude of 3 for an instant.

Notice that A and B are still the same amplitude, but now B is inverted.

For a moment the two wave pulses become one smaller wave pulse with an amplitude of (+2 + -1 = +1) positive one. This is Destructive Interference

These two wave pulses are going to collide. What will happen?

And after they pass…And after they pass…

ConstructiveConstructiveresults in a larger amplitudelarger amplitude

Types of InterferenceTypes of Interference

DestructiveDestructiveresults in a smaller amplitudesmaller amplitude

adding waves

NOW: NOW: You will practice wave You will practice wave calculations as well as calculations as well as review springs & review springs & pendulums: pendulums: PSE #1-12 and 1-4PSE #1-12 and 1-4DUE EOC TODAY!!!DUE EOC TODAY!!!THEN:THEN:

You will finish your word find so You will finish your word find so you can start you can start Wiggler Lab next Wiggler Lab next classclass!! (!! (due EOC next classdue EOC next class))