Introduction to WavesIntroduction to Waves

Vocabulary

9/11 – Volume

9/12 – wave

9/13 - crest

I can….

9/11 – Contrast mass and volume.

9/12 – Name & define 2 shapes of waves.

9/13 – Contrast electromagnetic waves and mechanical.

• Define a wave.• Draw a wave with the resting position drawn.• Label the wave – crest, trough, amplitude, wavelength• Define a medium and give an example.• Explain the relationship between amplitude and

energy.• Explain how to calculate frequency.• Explain the relationship between frequency and

energy.• NOW HOW DO YOU FEEL?

Why Do We Care About Radio Waves?

• Gadgets- cell phones, microwaves, remote controls, garage door openers

• Science- radio astronomy, atmospheric research

What’s in a Wave?• Wave – a rhythmic disturbance that transfers

energy through matter or space

Carries energy without transporting matter Carries energy without transporting matter from place to placefrom place to place

24.2 What is a wave?• A wave is an oscillation that travels from

one place to another.• If you poke a floating ball, it oscillates up

and down.• The oscillation spreads outward from where

it started.

What is a wave?

• Spreading of disturbance from one place to another.

• The source is a vibration or oscillation.

• Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points

Basic properties of wavesBasic properties of waves :• 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.

A wave does NOT carry matter with it! It just moves the matter as it goes through it.

What is a Medium?

• Medium – A substance or material that carries the wave.

• It does not make the wave – It carries the wave.

• EX – water, air, wall, people

Wave Types(shape)• A wave is a traveling disturbance that transfers energy.

• 2 Types of Waves:

– Transverse: wave sending vibration perpendicular to the

medium

– Longitudinal: push & pull wave sending vibration parallel to the medium

Parallel Vibration

Perpendicular Vibration

Direction of Energy

Direction of Energy

Wave Types1. Transverse waves: Waves in which the medium moves

at right angles to the direction of the wave

Transverse Waves

• Transverse waves – matter moves in the medium back and forth at right angles to the direction that the wave is traveling– Light waves & water waves

Transverse Waves Examples• Transverse Examples: These waves can travel without a MEDIUM!

– Ocean Waves – All Electromagnetic Radiation (comes from sun)

• Radio Waves• Microwaves• Infrared (heat waves)• Visible Light• UV Rays• X-rays• Gamma Rays

– The only difference

between all EM wave

types is a change in

wavelength, frequency

and energy.

Longitudinal waves or Compressional waves

• The oscillations of a longitudinal wave are in the same direction that the wave moves.

Longitudinal or Compressional Waves

• Compressional waves – matter in the medium moves back and forth in the same direction that the wave travels– Sound waves

Longitudinal Waves

• Longitudinal Examples: These waves REQUIRE a MEDIUM to travel!– Sound Waves

• Cannot travel in space (no medium/matter)

• Change in amplitude = volume

• Change in wavelength = pitch

Seismic Waves

• Seismic waves – combination of transverse and compressional waves which carry energy along and through Earth

The Slinky Coil

Play with the slinky. Make a transverse and compressional wave.

TYPES OF WAVESTYPES OF WAVES

Waves Waves are classified into different types according to their nature:

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.

• A disturbance is transmitted from one layer to the next through the medium. Can be transverse or longitudinal.

Examples: Water waves, sound, vibration of spring, etc.

Electromagnetic Waves• Waves from the Sun!

• Can travel through vacuum or a medium

• Disturbance of electric and magnetic fields travelling through space.

• All electromagnetic waves are transverse waves.

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

E-M Spectrum

E-M Spectrum

Wave Basics

Key Vocab.-Amplitude: The maximum displacement of a wave from equillibrium (height of a wave)-Wavelength: The length of one full wave cycle or repetition -Period: The amount of time it takes a wave to complete one full cycle-Frequency: The number of wave vibrations/repetitions per second (Hz)-Equilibrium: The resting place of a wave with no disturbance-Crest: The highest point or peak of a wave-Trough: The lowest point or bottom of a wave

Crest

Trough

Line of Equilibrium

Parts of a wave• You can think of a wave as a moving series of

high points and low points.• A crest is the high point of the wave.• A trough is the low point.

The Parts of a Wave

• Crest – the highest points of a wave

• Trough – the lowest points of a wave

Wave TrainWave Train- Two or more waves together.

Amplitude and Energy• Amplitude – the energy carried by a wave or how

high the wave is; related to the amount of energy

– For compressional waves it’s the amount of compression in the wave

– Example: The higher the wave, the more energy (THINK on ocean waves)

AMPLITUDE (A)• Maximum Displacement from the rest or central position.

• Transverse – measure half way between the crest and trough.

• Longitudinal – the higher the amplitude the closer the particles are together.

displacement

distance along rope

crest crest

trough

amplitude

amplitude

24.2 Parts of a wave

• The amplitude of a water wave is the maximum height the wave rises above the level surface.

Amplitude

• Bright light has a higher amplitude than low light.

• Tsumani has more amplitude than a beach wave.

Wavelength• Wavelength – the distance between one

point on a wave and the nearest point just like it

Wavelength (λ)The distance between two successive points of the same phase. Example: distance between two crests. SI unit: metre (m).

displacement

distance along rope

crest crest

trough

λ

amplitude

amplitude

Parts of a wave• Wavelength is the distance from any point

on a wave to the same point on the next cycle of the wave.

• The distance between one crest and the next crest is a wavelength.

Parts of a wave• The frequency of a wave is the rate at

which every point on the wave moves up and down.

• Frequency means “how often”.

Frequency and Period

• Frequency – the number of waves that pass a given point each secondMeasured in Hertz = 1/sec Period: The amount of time it takes one wavelength

to pass a point

Frequency Relationships• (velocity of waves) = (wavelength) x (freq.)

– As wavelength gets smaller frequency goes up

– As wavelength gets bigger frequency goes down

– As velocity gets higher, frequency goes up

– As velocity gets lower, frequency goes down

Wave Speed

• The speed of a wave depends on the properties of the medium it is traveling through– In general sound waves travel the fastest through

solids then liquids then gases– Light waves travel the fastest in empty space and

slowest through solids– Sound waves travel faster through warmer

mediums

The speed of waves

• A wave moves one wavelength in each cycle.

• Since a cycle takes one period, the speed of the wave is the wavelength divided by the period.

Calculating Wave Speed

• Speed = wavelength x frequency

• V = λ x f

• V = velocity (m/s)

• λ = wavelength (m)

• f = frequency (Hz; 1/sec)

Wave speed: Depends on the medium in which the wave is traveling. It varies in solids, liquids and gases.

A mathematical way to calculate speed:

wave speed = wavelength x frequency

(in meters) (in Hz)

OR

v = f x ג

Problem: If a wave has a wavelength of 2 m and a frequency of 500 Hz, what is its speed?

The speed of waves• The speed is the distance traveled (one wavelength)

divided by the time it takes (one period).

• We usually calculate the speed of a wave by multiplying wavelength by frequency.

Period (T)

• Time taken to generate one complete wave (or to complete one cycle)

• SI unit: second (s)

fT

1

As f increases, T decreases

Relationship between T and f

The speed of waves

• The speed of a water wave is how fast the wave spreads, NOT how fast the water surface moves up and down or how fast the dropped ball moves in the water.

How do we measure the wave speed?

Example #1

• What is the speed of a wave with a wavelength of 2m and a frequency of 3 Hz?

V = λ x f

V = (2)(3)

V = 6 m/s

Example #2• A wave is traveling at a speed of 12 m/s and

its wavelength is 3m. Calculate the wave’s frequency.

V = λ x f

12 = (3)(f)

12 = f

3

4 Hz = f

Four wave interactionsWhen a wave encounters a surface, four interactions can occur:

1.reflection,

2.refraction,

3.diffraction, or

4.absorption.

BEHAVIORS OF WAVES

Standard 8-6.4

Summarize the behaviors of waves (including refraction, reflection, transmission and absorption).

VOCABULARY WORDS:

4 Ways that waves interact

1. Reflection: When a wave hits a surface through which it cannot pass, it bounces back.

2. Refraction: Is the bending of a wave as it moves from one medium into another medium at an angle, it changes speed as it enters the second medium, which causes it to bend.

3. Transmission• Occurs when waves pass through a given point or

medium. example: Sound waves transmitted thru solids, liquids and gases.

Radio waves are transmitted through one electron through another.

• Light waves are transmitted – 3 ways light and matter can pass through material.

A. Transparent material: Only a small amount of light is reflected or absorbed (may be clear or colored material such as filters, windows).

B. Opaque material: allows no light waves to be transmitted through them.

C. Translucent materials: Transmit some light, but cause it to be scattered so no clear image is seen.

4. Absorption- Occurs when the energy is not transferred through

or reflected by the given medium• Disappearance of an electromagnetic wave into a

medium. – Opposite of reflection

• We see colors because of the selective absorption of visible light.– Objects absorb certain wavelengths and we see what is

leftover.

– The colors we see depend on the wavelength absorbed.

Absorption

Orange

Yellow GreenBlue

Violet

RedRed

The apple absorbs all wavelengths except red.

The apple reflects mostly red. Therefore, it looks like red.

Essay question on test!!!

Absorption• A material that absorbs all wavelengths of visible

light will appear black.

• In contrast, a material that reflects all wavelengths will appear white.

• Objects or substances that absorb any wavelength of EM radiation become warmer and convert the absorbed energy to infrared radiation. (GREENHOUSE EFFECT)

1. WHAT ARE THE 4 WAYS WAVES WILL INTERACT?

Reflection

Refraction

Transmission

Absorption

2. WHAT ARE THE 3 WAYS LIGHT AND MATTER CAN PASS THROUGH? Transparent

Opaque

Translucent 3. WHAT IS THE COLOR WHITE AND THE COLOR BLACK?

White is all color reflected

Black is all color absorbed

DIFFRACTION: Is the scattering of a wave as it hits the edges of a boundary or tiny opening. The wave will try to curve around the boundary or outward through the opening.

EM (Electromagnetic Waves)• How do electromagnetic waves differ from

mechanical waves?

– EM waves do NOT need a medium to travel through.

EM Waves

• Every time you feel the sun’s heat, listen to your MP3 player, or pop a bag of popcorn in the microwave, you are using a different form of the electromagnetic energy.

• EM waves make these events possible.

EM Waves

• EM waves are transverse waves that have some electrical properties and some magnetic properties.

• It consists of changing electric and magnetic fields.

• EM waves travel as vibrations in electric and magnetic fields.

EM Waves• EM waves vary based on wavelength, energy

and frequency.

• Electromagnetic energy is created by vibrations (just like mechanical waves).– This produces waves that carry the energy.

• Each EM wave emits at different energy levels.– The collection of all EM frequencies is known as

the “Electromagnetic Spectrum”.

Electromagnetic Spectrum

Electromagnetic Spectrum1. Radio waves are used to transmit radio and

television signals. Radio waves have wavelengths that range from less than a centimeter to tens or even hundreds of meters.

– Longest wavelength, lowest frequency and least amount of energy.

– They travel long distances by reflecting their signals off Earth’s atmosphere or off satellites.

2. Microwaves – shorter wavelengths, higher frequencies, and more energy than radio waves.– Cell phones and radar are two uses of microwaves.

3. Infrared Light - is the region of the electromagnetic spectrum that extends from the visible region to about one millimeter (in wavelength). Infrared waves include thermal radiation. – Associated with heat

Electromagnetic Spectrum

4. Visible Light – The range of EM waves that can be detected by the human eye.– Longest wavelength is of visible light is red.– Shortest wavelength of visible light is violet.

• The color we see is determined by the way the light interacts with the object.– How it is reflected and how it is transmitted.

• 400 – 700 nm (nanometers)

Electromagnetic Spectrum

Each of these colors actually corresponds to a different wavelength of light.

Visible Light

How Roy G. Bv Lost a Vowel

The sequence of colors red, orange, yellow, green, blue, and violet may be remembered by memorizing the name of that fine fellow

"ROY G. BV". This was originally "ROY G. BIV", because it used to be common to call the region between blue and violet "indigo". In modern usage, indigo is not usually distinguished as a separate color in the visible spectrum; thus Roy no longer has any vowels in his last

name.

Electromagnetic Spectrum

5. Ultraviolet Light (UV)- Higher frequency than visible light and carry more energy.– Can damage or kill living cells– Tan skin by the sun or tanning bed

Electromagnetic Spectrum6. X-rays - high energy waves which have great

penetrating power and are used extensively in medical applications and in inspecting welds. The wavelength range is from about ten billionths of a meter to about 10 trillionths of a meter.

– Short wavelengths and high frequencies allow them to travel through skin, but not bone (more dense)

Electromagnetic Spectrum

7. Gamma Rays – Shortest waves, with the highest frequency (and highest energy).– They are more penetrating than X-rays– Can kill living cells– Used to sterilize medical equipment

How do prisms separate visible light?• When light shines through a prism, the glass changes

the behavior of each light wave according to the wave's wavelength.

• This property of glass is known as its refractive index.

• The prism changes the direction the light is traveling.

• As a result, what goes in as ordinary white light comes out separated into a spectrum of different colors.

• That's because white light is really all those wavelengths mixed together.

Each of these colors actually corresponds to a different wavelength of light.

Visible Light

How Roy G. Bv Lost a Vowel

The sequence of colors red, orange, yellow, green, blue, and violet may be remembered by memorizing the name of that fine fellow

"ROY G. BV". This was originally "ROY G. BIV", because it used to be common to call the region between blue and violet "indigo". In modern usage, indigo is not usually distinguished as a separate color in the visible spectrum; thus Roy no longer has any vowels in his last

name.

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

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

characteristics

Answer: speed = 2 m x 500 Hz = 1000 m/s

Changing Wave Direction1.Reflection: When waves bounce off a surface.

If the surface is flat, the angle at which the wave hits the surface will be the same as the angle at which it leaves the surface (angle in = angle out).

This is the law of reflection.

A travelling wave is reflectedreflected when it hits a barrier.

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

Reflection of Waves

Reflectedwaves

Reflectedwaves

Reflector

2. Refraction: Waves can bend.

This happens when a wave enters a new medium and its SPEED CHANGES.

The amount of bending depends on the medium it is entering.

Refraction of WavesRefraction of Waves

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

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

3. Diffraction: The bending of waves AROUND an object.

The amount of bending depends on the size of the obstacle and the size of the waves.

Large obstacle, small wavelength = low diffraction

Small obstacle, large wavelength = large diffraction

Diffraction of Waves

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

The wavelength of the wave is not changed in diffraction.

Interference of Waves

When two or more waves propagating in the same medium meet at the same point, interference is said to occur. A stable interference pattern can be observed when two water waves of same frequency meet one another in a ripple tank.

=

24.2 Wave interactions

• Diffraction usually changes the direction and shape of the wave.

• When a plane wave passes through a small hole diffraction turns it into a circular wave.

Do these on your own

• A tuning fork has a frequency of 280 Hertz and the wavelength of the sound produced is 1.5 meters. Calculate the velocity of the wave.

• A wave is moving toward shore with a velocity of 5.0 m/s. If its frequency is 2.5 hertz, what is its wavelength?

SUMMARY

FOOD FOR THOUGHT

• In space films, we often hear the sound of the engine of the spaceship as the zoom past each other in outer space. We even hear the spaceship firing lasers at one another. What is seriously wrong in the films?

FOOD FOR THOUGHT

• Why don't incoming ocean waves bring more water on to the shore until the beach is completely submerged?

What is this “photon” term you’re throwing in there?

• A photon is a bundle (quantum) of light

• A photon has energy equal to

Recall that

h is Plank’s constant

ν is the frequency of the radiation (wave)

hE

What does a photon do?

• Both magnetic and electric forces involve the exchange of photons

• The photon has zero rest mass, but has momentum, can be deflected gravity, and can exert a force

The Electromagnetic Spectrum

• Think you know all about the electromagnetic spectrum? Well take a tour of the Electromagnetic Spectrum to find out more cool information. Then, if you’re brave enough, take the electromagnetic quiz. Remember to run the applet at the top of the page.

• If you still need more help review the next 7 slides. If not click

TYPES OF ELECTROMAGNETIC WAVES

GAMMA RAYS

• Emitted from the nuclei of atoms during radioactive decay or during high-speed collisions with particles.

• Ionizing

• Used in cancer treatment and for sterilization Sources: Cobalt 60, the inner core of the sun

X-RAYS• Emitted when an electron

moves from certain excited states back down to its ground state, or when an electron that is moving very quickly is suddenly stopped

• Two groups - long wavelength (soft x-rays) and shorter wavelength (hard x-rays)

• Used for radiography (x-ray photography) and to look at materials in industry for defects

• Sources:  emitted by heavy atoms after bombardment by an electron

ULTRAVIOLET

• Above the color violet  • Three groups - UV A, UV

B, and UV C. • “A” type: longest

wavelength; least harmful • UV B and UV C are

absorbed by DNA in cells • Used by the body to

produce vitamin D, to kill bacteria on objects, and for sun tanning

• Sources:   Ultra hot objects 5000°C or more

VISIBLE LIGHT

• White light: combination of all the colors

• Rainbow: example of white light that has been separated into a continuous spectrum of colors

• The names of colors are assigned in order of their wavelengths

• Used for communications

(fiber optics)• Sources:   very hot

objects

Color Wavelength interval Frequency interval

red ~ 625 to 740 nm ~ 480 to 405 THz

orange ~ 590 to 625 nm ~ 510 to 480 THz

yellow ~ 565 to 590 nm ~ 530 to 510 THz

green ~ 520 to 565 nm ~ 580 to 530 THz

cyan ~ 500 to 520 nm ~ 600 to 580 THz

blue ~ 430 to 500 nm ~ 700 to 600 THz

violet ~ 380 to 430 nm ~ 790 to 700 THz

INFRARED

• Thought of as heat but is not always

• Far infrared energy is heat energy.

• All objects that have warmth radiate infrared waves

• Easily absorbed and re-radiated. 

• Used in remote controls,  surveillance, therapy of muscles

• Sources:  Humans, the sun

MICROWAVES

• 1 mm-1 dm in length • Absorbed by water

molecules – how microwave ovens heat food

• Used in telecommunications and power transmission

• Sources:  electric circuits, many stars, microwave ovens

RADIO WAVES

• 10 cm- 100,000+m  in length

• Only cosmic waves the reach the surface of the Earth

• Cause of noise• Divided into smaller

frequency dependent groups called bands  

• Used for communications

• Sources:  transmitters and sparks from motors

Polarization

• Electric and magnetic fields which make up wave have preferred direction

• Can be horizontal, vertical, circular, or elliptical

• Most radio emission is unpolarized

• To learn more click here

Polarization

x

yElectric Field

Magnetic Field

Electromagnetic Wave

x

y

zE

Horizontal Polarization

Electric Field

Magnetic Field

Electromagnetic Wave

x

y

z

E

Vertical Polarization

• 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: Hertz (Hz)

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

The Wave EquationThe Wave EquationThe wave velocity is the distance traveled by the wave in one second ……....

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

v = ƒv = ƒ

Using the Wave EquationUsing the Wave EquationExample :

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

The answer is…

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……

By using the wave

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