8/13/2019 07 Waves I - Waves

1/51

Physics I onors 1

Waves and SoundWave Characteristics

8/13/2019 07 Waves I - Waves

2/51

Physics I onors 2

Transferring Energy Without Transferring

Matter

Vibrating bodies connected to their environment

will transfer energy to the environment.

The vibrations are then transferred though the

environment from neighbor to neighbor.

This energy transfer is called wave motion.

Wave motion moves energy through a medium

without moving the whole medium. Only theshape or formof wave travels, not the

medium.

8/13/2019 07 Waves I - Waves

3/51

Physics I onors 3

Definition of wave

Aperiodicdisturbance which travels through a

medium from one point in space to the others.

Wave motion means the propagation of waves through

a medium.

8/13/2019 07 Waves I - Waves

4/51

Physics I onors 4

TYPES OF WAVESWaves are classified into different types

according to their natures :

Transverse waves Longitudinal waves

Mechanical waves

Transverse waves

Electromagnetic waves

WAVES

8/13/2019 07 Waves I - Waves

5/51

Physics I onors 5

Three types of waves:

Mechanical wavesrequire a material medium to

travel (air, water, ropes).

Electromagnetic wavesdo not require a mediumto travel (light, radio).

Matter wavesare produced by electrons and

particles.

8/13/2019 07 Waves I - Waves

6/51

Physics I onors 6

Electromagnetic Waves

Material medium is not essential for propagation. e/mwaves travel through vacuum.

Disturbance of electric and magnetic fields travelingthrough space.

All electromagnetic waves are transverse waves.

8/13/2019 07 Waves I - Waves

7/51

Physics I onors 7

Electromagnetic Waves

Light Waves

Radio Waves

X-Rays

No MediumRequired

Travels At TheSpeed Of Light

3 X 108m/s in a

vacuum Cannot Be

Observed

8/13/2019 07 Waves I - Waves

8/51

Physics I onors 8

Matter Waves

Matter is in the form of particles.

Energy is in the form of waves.

Energy can be quantized and matter can have awavelength.

Matter displays wavelike properties.

8/13/2019 07 Waves I - Waves

9/51

Physics I onors 9

Mechanical Waves

Transverse waves cause the medium to moveperpendicular to the direction of the wave.

Longitudinal waves cause the medium to moveparallel to the direction of the wave.

Surface wavesare both transverse waves andlongitudinal waves mixed in one medium.(Such as water waves)

Torsional wavesproduce a twisting motionthrough the mediumsuch as the ones whichcaused the collapse of the Tacoma NarrowsBridge.

http://members.tripod.com/~tacomaweekly/NarrowsBridge.htmlhttp://members.tripod.com/~tacomaweekly/NarrowsBridge.htmlhttp://members.tripod.com/~tacomaweekly/NarrowsBridge.htmlhttp://members.tripod.com/~tacomaweekly/NarrowsBridge.html

8/13/2019 07 Waves I - Waves

10/51

Physics I onors 10

3 Types of Mechanical Waves

8/13/2019 07 Waves I - Waves

11/51

Physics I onors 11

Transverse Wave

8/13/2019 07 Waves I - Waves

12/51

Physics I onors 12

Transverse Waves

These waves cause particles of a medium to vibrate

perpendicular to the direction of motion

The waveform appears in the shape of sine curve.

8/13/2019 07 Waves I - Waves

13/51

Physics I onors 13

Longitudinal Waves

These waves cause medium to vibrate in a direction

parallel to the direction of motion.

8/13/2019 07 Waves I - Waves

14/51

Physics I onors 14

Longitudinal Waves

Speaker membrane expands, creating a region where the airmolecules are packed closely together, a"condensation". The air pressure in a condensation is higherthan normal.

As the membrane moves back, a regionis left behind where few molecules arelocated, a "rarefaction". Meanwhile, thecondensation moves forward.

8/13/2019 07 Waves I - Waves

15/51

Physics I onors 15

Surface Waves

Waves out on the ocean's surface are acombination of transverse and longitudinal

waves.

The wave height is the distance from a trough to

a peak and the wavelength is the peak to peak

distance.

When the wave height is

1/7 the wavelength

the wave breaks.

8/13/2019 07 Waves I - Waves

16/51

Physics I onors 16

Tacoma Narrows Bridge

Torsional Oscillation

8/13/2019 07 Waves I - Waves

17/51

Physics I onors 17

Period: T Frequency: f

The PERIODis the time

for a particle of the

medium to complete one

oscillation.

The SI unit for period isthe second

The FREQUENCYof is

the number of cycles per

unit time.

The frequency of a wave is

equal to the number of

waves that pass aparticular point in one

second.

The unit is Hertz (Hz)

which is a cycle persecond.

FREQUENCYis also the

reciprocal of the period.

8/13/2019 07 Waves I - Waves

18/51

Physics I onors 18

Period and Frequency

Tf

1

fT

1

8/13/2019 07 Waves I - Waves

19/51

Physics I onors 19

Amplitude: A

The AMPLITUDEof a wave is the maximum

distance of a particle from the equilibrium

position.

The SI unit for amplitude is meter

8/13/2019 07 Waves I - Waves

20/51

Physics I onors 20

Amplitude: A

The energy content of a wave is indicated

by the amplitude.

Two waves of the same frequency can have

different amplitudes.

The greater the amplitude, the more work a

wave can do.

Amplitude does not affect wavelength,

frequency or velocity

8/13/2019 07 Waves I - Waves

21/51

Physics I onors 21

Wavelength:

The WAVELENGTHof a wave is the lengthof one complete cycle.

It is the distancebetween twoconsecutive in phase

points.

In phasepoints arethose that are movingin step with eachother.

8/13/2019 07 Waves I - Waves

22/51

Physics I onors 22

Comparing waves

8/13/2019 07 Waves I - Waves

23/51

Physics I onors 23

Wave Velocity

The speed of a wave is the product of thewaves frequency and wavelength.

The speed does not depend on amplitude or

frequencyit depends on the properties of

the medium.

Sound waves depend on temperature of the

air and water waves depend on depth of

water.

fv

8/13/2019 07 Waves I - Waves

24/51

Physics I onors 24

Do you remember..?

4. The periodic wave

in the diagram below

has a frequency of 40.hertz.

What is the speed of

the wave?

a. 13 m/s b. 60.

m/s c. 27 m/s d.

120 m/s

8/13/2019 07 Waves I - Waves

25/51

Physics I onors 25

More to remember..

Austin drops a stone into a dry well 175 m

deep. How long, after he drops the stone,

does he hear it hit the bottom of the shaft? The speed of sound waves is 340 m/s.

Assume g = 10 m/s/s

8/13/2019 07 Waves I - Waves

26/51

8/13/2019 07 Waves I - Waves

27/51

Physics I onors 27

Waves and SoundWave Actions

8/13/2019 07 Waves I - Waves

28/51

Physics I onors 28

Waves and Boundaries

When a wave encounters an interface (boundary), it

may be reflected and/or transmitted!

An incident wave goes into a new medium as a

transmitted wave and bounces back as a reflectedwave.

Density difference determines how much of the wave

is transmitted and how much is reflected.

8/13/2019 07 Waves I - Waves

29/51

Physics I onors 29

Waves and Boundaries

Small Difference Between the Densities ofthe two Media

Most of wave is transmitted.

Amplitude of transmitted wave will be greater

than amplitude of reflected wave.

Large Difference Between the Densities of

the two Media

Most of incident wave is reflected.

Amplitude of reflected wave is greater than

amplitude of transmitted wave.

8/13/2019 07 Waves I - Waves

30/51

Physics I onors 30

Less Dense to More Dense Medium

When a wave hits the boundary of a more dense

medium, the reflected wave is inverted.

8/13/2019 07 Waves I - Waves

31/51

Physics I onors 31

More dense to a Less Dense Medium

When a wave hits the boundary of a less dense

medium, the reflected wave is erect.

8/13/2019 07 Waves I - Waves

32/51

Physics I onors 32

Reflection of Waves

A traveling wave isreflectedwhen it hits a barrier.

This phenomenon can easily be observed when a traveling

water wave hits a reflector in the ripple tank.

Reflected

waves

Reflector

8/13/2019 07 Waves I - Waves

33/51

Physics I onors 33

Law of Reflection

When an incident wave encounters a boundary at anangle, , from the normal, its reflected wave will

be reflected at the same angle from the normal.

8/13/2019 07 Waves I - Waves

34/51

Physics I onors 34

Do you remember???

What is a boundary?

What determines the speed of a wave?

What happens to a wave hitting a boundary?

How do you know if a wave will reflect

erect or inverted?

What does not change at a boundary?

What must change at a boundary?

8/13/2019 07 Waves I - Waves

35/51

Physics I onors 35

When a wave passes into a new medium

Itswavelengthchanges Itsspeedchanges with density

Itsfrequencyremains the same

8/13/2019 07 Waves I - Waves

36/51

Physics I onors 36

Refraction

Refraction is the bending of a wave as it passes from

one medium to another medium of different

propagation speed.

8/13/2019 07 Waves I - Waves

37/51

Physics I onors 37

The Densities of the Media

If the light passes from a less dense to a more

dense medium, it bends toward the normal.

If the light passes from a more dense to a lessdense medium, it bends away from the normal.

8/13/2019 07 Waves I - Waves

38/51

Physics I onors 38

Refraction of Waves

The speed of a water wave increases with

depth.

This change in speed is accompanied by

refraction.

8/13/2019 07 Waves I - Waves

39/51

Physics I onors 39

Diffraction

Diffraction is the spreading of a wave disturbance

around and beyond the edge of a barrier.When a traveling water wave hits an obstacle, the

wave fronts spreads out round the edge andbecomes curved.

The wavelength of the wave is not changed indiffraction.

S iti P i i l

8/13/2019 07 Waves I - Waves

40/51

Physics I onors 40

Superposition Principle

Wave interferenceoccurs when two or more wavesact simultaneously on a medium.

Whenever two or more waves pass through each

other, the resulting disturbance at a given point in

the medium may usually be found by adding theindividual displacements that each wave would

have caused. (Principle of Superposition)

= +

8/13/2019 07 Waves I - Waves

41/51

Physics I onors 41

Principle of Superposition

The displacement of a medium caused by two or

more waves is the algebraic sum of thedisplacements caused by the individual waves.

When colliding waves combine (add) the result can

either be bigger or smaller than the original waves.The waves add constructively or destructively

depending on the relative sign of each wave.

8/13/2019 07 Waves I - Waves

42/51

Physics I onors 42

Superposition & Interference

Consider two harmonic wavesAandB

meeting atx = 0. The displacement versus time for each is

shown below:

CONSTRUCTIVE

INTERFERENCE

DESTRUCTIVE

INTERFERENCE

8/13/2019 07 Waves I - Waves

43/51

Physics I onors 43

Constructive Interference

8/13/2019 07 Waves I - Waves

44/51

Physics I onors 44

Constructive Interference

Occurs when wave displacements are in phase.

Two waves combine to create a larger wave.

Constructive interference occurs when the

waves are trying to displace the medium inthe same direction.

More than one wave can occupy the same

space at the same time.

8/13/2019 07 Waves I - Waves

45/51

Physics I onors 45

Destructive Interference

Occurs when wave displacements are opposite in

phase.

One wave cancels the other out.

8/13/2019 07 Waves I - Waves

46/51

Physics I onors 46

Destructive Interference

When these two waves are completelyoverlapping, there will be complete destructiveinterference.

Destructive interference occurs when the wavesare trying to displace the medium in oppositedirections.

8/13/2019 07 Waves I - Waves

47/51

Physics I onors 47

Before and AfterWaves have the ability to pass through one another

and not change.

8/13/2019 07 Waves I - Waves

48/51

8/13/2019 07 Waves I - Waves

49/51

Physics I onors 49

Interference in Water Waves

8/13/2019 07 Waves I - Waves

50/51

Physics I onors 50

Standing Wave in Action

Nodes are places on a standing wave that do not

appear to move.Antinodes are places on a standing wave that are the

greatest displacement from equilibrium.

8/13/2019 07 Waves I - Waves

51/51

51

Standing Waves

Waves traveling in opposite directions, with

the same frequency, wavelength, and

amplitude, produce a standing wave.