1

Watch Video

“What do these things have in common?”

“Waves”What are they?

Where do they come from?

How are the made?

Good/Bad

Do “The Wave”

2

Waves

Introduction to

Read Pg 335 (pdf 46)

3

Waves are caused by vibrations and carry energy from one place to another and effect changes.

These changes can be extremely useful or can cause tremendous damage.

Wave: a disturbance that repeats itself regularly in space and time and transmits progressively from one particle of matter to the next, without transporting the matter.

4

The wave is an essential unifying concept of modern physics. Matter and energy both share wave properties

Take for example what is known as the electron wave partial duality theorem. Which says that an electron can exist as a wave or as a particle.

In quantum physics all matter theatrically can be expressed as a wave. This is part of the premise of transportation. By having the ability to change mass into its wave function and then reassemble it in a new location.

On The Side

5

Just a Few Examples of Waves

ocean waves

sound waves

light waves

earthquakes

TV and radio waves

microwave ovens

X-rays

fiber optics

lasers

6

Wavelength: the distance between two successive wave crests, the symbol for wavelength is lambda. ( λ )

Crest : the high point of the wave.

Trough: the low point of the wave.

Amplitude: the distance from the midpoint or rest position of the wave to either the crest or trough of the wave.

7

Spring Demo

8

Classification of Waves

All waves can be classified as being either a mechanical wave or an electromagnetic wave.

Mechanical waves: This type of wave requires medium material. Examples, water waves, sound waves, or waves on a rope.

Electromagnetic waves: This type of wave does not require medium material. Examples, light waves, radio waves, X-rays.

9

Mechanical waves can be broken down further into two subcategories of waves.

Transverse wave: Waves that cause particles over which they pass to vibrate at right angles to the direction in which the waves are moving.

Example: picture a boat bobbing up and down in the water as a wave passes by.

Spring Demo

10

Longitudinal wave: Waves that cause particles over which they pass to vibrate parallel to the direction in which the waves are moving.

Example: sound wave, which we will examine with greater detail later in this chapter.

Spring Demo

11

Transverse vs Longitudinal

Video clip

12

Waves

Mechanical Electromagnetic

Transverse Longitudinal

Water Sound

Transverse

Light

13

http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

Some Cool Sites

http://phet.colorado.edu/index.php

http://www.edumedia-sciences.com/en/a251-transverse-wave

14

Wave pulse: A single pulse caused by a single disturbance or vibration. A constant vibration would then produce a series of continuous pulses referred to as a wave.

See phet site

15

Period: The time for one complete cycle, or vibration. The symbol for period is ( T ).

Frequency: The number of cycles or vibrations that occur in one second. The units of frequency are Hertz. ( Hz ). 1 Hz is one vibration in one second. The symbol for frequency is ( f ).

Period and frequency are related by the following equation.

Tf

1

16

Example: A sound wave has a frequency of 262 Hz. What is the period of the wave?

3.82 x 10-3 sec

17

Example: A mass oscillates up and down on on a spring. If the mass completes 37 cycles in a 60 second period. What is both the frequency and period of the oscillating mass.

f = 0.62 Hz and T = 1.62 sec

18

Do#’s 1- 4, Pg 341 (pdf 48)

19

The Universal Wave Equation

vd

t

The universal wave equation helps us to determine wave speed, by starting with the general relationship between velocity distance and time.

Now lets modify this for waves.

20

vT

A waves will travel a certain amount of distance, let’s say one wavelength, in a certain amount of time.

The amount of time for one full wavelength to go by is what we define as the period of a wave.

Therefore the standard equation for velocity can be rewritten and as follows.

vd

t

21

Now using the relationship between period and frequency we get.

vf

1

rearrange and simplify to get

v fthis is known as the Universal wave equation and relates velocity, wave length, and frequency of a wave.

22

Example: A sound wave with a frequency of 262 Hz has a wavelength of 1.29 m. What is the speed of the sound wave?

1.29 262

338

v f

m s

23

Example: A sound wave produced by a clock chime 515 m away is heard 1.50 sec later.

a) What is the speed of sound in air?

515

1.5343

dv

t

m s

b) If the sound wave has a frequency of 436 Hz. What is its period?

1

1

4362.29

Tf

ms

c) What is his wavelength?

343

4360.787

v f

v

f

m

26

Example: A hiker shouts towards a vertical cliff 695 m away. The echoes heard 4.00 sec later.

a) What is the speed of sound in air?

695

2.00348

dv

t

m s

b) The wave length of the sound is 0.750 m. What is the frequency?

347.5

.750463

v f

vf

f

Hz

c) What is the period of the wave?

1

1

4632.16

Tf

ms

29

Example: A radio wave, a form of an electromagnetic wave, has a frequency of 99.5 MHz. What is its wavelength?

8

6

3 10

99.5 103.02

v f

v

f

x m s

x Hzm

30

Example: A typical light wave has a wavelength of 580 nm.

a) 5.8 x 10-7 m

b) What is the frequency of the wave?

a) What is the wavelength of the light in meters?

8

7

14

3 10

5.8 10

5.2 10

v f

vf

x m sf

x m

x Hz

31

Example: Water waves with wavelength 2.8 m, produced in a wave tank, travel at the speed of 3.80 m/s. What is the frequency of the vibrator that produced them?

3.80

2.81.4

v f

vf

m sf

mHz

32

Do # 5 – 9, Pg 349 – 350 (pdf 49)

33

Reflections of Waves

The characteristic of a wave striking a different medium and being bounced back, either totally or partially, is termed reflection.

34

The first is when the medium has a fixed end, or in other words the end in not allowed to move.

There are two different ways in which a wave pulse can be reflected.

In this case the reflected wave pulse is inverted.

35

The second way in which a wave can be reflected is when the end of the medium is open or the end is allowed to move.

In this case the reflected wave pulse is up right.

36

If the wave strikes the medium at an angle then we have a different story.

The wave will be reflected at an angle, this is know as the law of reflection.

See phet site

37

Do #’s 1-7, Pg 353 (pdf 49)

38

Law of Reflection:The angle of incidence to the normal is equal to the angle of reflection to the normal. The normal being a ray perpendicular to the surface.

39

40

Diffuse Reflection:This type of reflection is characteristic of a wave striking a rough surface and being reflected randomly (in all directions).

For example, paper reflects light in all directions, therefore you can read from any angle.

41

Sound Reflection:

The reflection of sound is sometimes referred to as an echo.

The percentage of sound reflected from a surface depends on the nature of the surface.

For example you get a high reflection rate from a rigid, smooth surface such as, Gym walls, and low reflection from a soft, irregular surface such as, soft irregular walls in a movie theater

42

The study of sound reflection is called acoustics.

43

Multiple sound reflections that cause sound to be garbled are called reverberations.

44

Interference of Waves

When two or more waves occupy the same space at the same time they are said to interfere with each other.

Since both waves are moving the interference will only last for a short length of time. At which point the two waves will continue on unchanged by the encounter.

For that period of time when the waves are interfering with each other they can do so in two distinct ways known as constructive interference and destructive interference.

45

Constructive interference results in a wave pulse that is bigger than either individual pulse. ( ie: they add together)

46

47

Destructive interference results in a wave pulse that is smaller than either individual pulse. ( ie: they subtract from each other)

48

See phet site

49

The principle of superposition may be applied to waves whenever two (or more) waves are travelling through the same medium at the same time.

The waves pass through each other without being disturbed.

The net displacement of the medium at any point in space or time, is simply the sum of the individual wave displacements. This is true of both waves or pulses.

Superposition of Waves

http://www.kettering.edu/~drussell/Demos/superposition/superposition.html

50

Example: Use the principle of superposition to determine the resultant wave.

51

Example: Use the principle of superposition to determine the resultant wave.

52

Standing WavesWhen many similar waves occupy the same medium there is a continuous interference pattern.

Which consists of both constructive interference and deconstruct interference.

Under ideal circumstances a standing wave can be established.

53

In actual fact there are many waves, all of which are moving, but the overall pattern caused by the interference simply gives the appearance of a stationary wave.

A standing wave is exactly as it’s name implies, a wave that appears to be motionless and is simply standing in one place.

54

There are two main parts to the standing wave. The nodes, this is the location of maximum destructive interference, and the anti-nodes, this is the location of the maximum constructive interference.

Video Clip

Ruben's Tube Experiment Physics Project

Tacoma Narrows Bridge Collapse

56

Do#’s 1 – 5, Pg 362 (pdf 50)

57

Refraction

The velocity of a wave is dependent only on the medium in which the way is traveling.

Therefore if you change the medium, the velocity of the wave will also change.

This change in velocity then causes a change in the direction of the wave.

58

This phenomenon is known as refraction.

http://www.physics.uoguelph.ca/applets/Intro_physics/refraction/LightRefract.html

http://physics.ham.muohio.edu/waveapplets/RefTest.html

60

Refraction can happen for either of the following circumstance

1) from a less dense to a more dense medium

When you run in to the water at the beach and you trip and fall forward.

2) from a more dense to a less dense medium

light going from water to air causes a stick to look bent or broken.

61

62

Refraction of light passing from air into glass

The ray of light entering the glass termed the incident ray.

The ray that travels in the glass is termed the refracted ray.

The angle between the incident ray and the normal is called the angle of incidence.

The angle between the refracted ray and the normal is called the angle of refraction.

63

64

The incident ray strikes the glass at an angle and the refracted ray is bent “towards the normal”.

Since the light ray bends towards the normal as it passes from air to glass (less dense to more dense), the angle of incidence is greater than the angle of refraction.

When the light leaves the glass the ray is deflected “away from the normal”. In this case the angle of refraction is greater than the angle of incidence. (more dense to less dense)

65

θi

θi

θr

θr

Air

Glass

66

Laws of RefractionFrom less dense to more dense medium the angle of incidence is greater than the angle of refraction.

From more dense to less dense medium the angle of refraction is greater than the angle of incidence.

67

A prism uses refraction to separate the various colors of light composing the visible spectrum.

This occurs because all the colors that make up white light do not travel at the same speed in glass thus causing each color to bend different amounts.

68

This color separation is referred to as dispersion.

Rainbows work because the water drops act as tiny prisms

69

Diffraction

You can usually hear a siren long before you see an emergency vehicle, because sound can “bend” around corners.

This characteristic of bending around a corner is not a characteristic just for sound but for all waves in general, and is known as the diffraction of waves.

70

Diffraction: The bending of waves around a barrier.

When a straight wavefront strikes a barrier the component of the wave that is allowed to pass through the barrier will then become bent and appear as a circular wave.

71

The amount of bending depends primarily on the width of the opening maximum bending occurs when the width of the opening is approximately one wave length.

http://www.ngsir.netfirms.com/englishhtm/Diffraction.htm

72

73

74

THE ENDPlease Read over Pg 371 in your text

Please do Pg 372&373

#’s

1, 2, 4, 5, 8, 9, 10, 11, 12, 14, 15,

16, 21, 22, 23, 24, 25, 27, 28.