Light travels in straight lines.

WAVE

• Carries energy from one place to another • Classified by what they move through

1. Mechanical Wavesthe energy is transferred by vibrations of medium (medium = substance or material which carries the wave)ex/ ocean waves move through water

2. Electromagnetic waves (EM Waves)the energy moves through disturbances in the electromagnetic field.

a disturbance that transfers energy

MECHANICAL WAVES

travel through & gradually lose energy to that medium

• Examples:– water, sound, rope, &

spring waves

• Mechanical Media:– water, air, rope, spring

require a medium (the material through which the

disturbance is moving) to transmit energy

Making a pulse

ELECTROMAGNETIC WAVES

The wave, or "disturbance," is in an invisible thing called the electric force field.

Examples:– Radio waves, microwaves, light, x rays, gamma

rays

They can travel through empty space.

Don’t require a medium (the material through which the disturbance is moving) to transmit energy

For more information and interactives go tohttp://www.colorado.edu/physics/2000/waves_particles/

Electromagnetic Waves

• They travel as vibrations in electrical and magnetic fields. • Have some magnetic and some

electrical properties to them.

• Called transverse waves, wave motion is perpendicular to the direction the energy moves– http://einstein.byu.edu/~masong/htmstuff/WaveTrans.html– http://hermes.ffn.ub.es/~albert/ones/wavemotion.html

Electromagnetic Waves

Electromagnetic Waves

• Light is an electromagnetic wave• A transverse wave that does not

require a medium, therefore it can travel through space

• Light can travel through certain media

• Light is part of a range of electromagnetic waves known as the electromagnetic spectrum

TRANSVERSE WAVE STRUCTURE

CREST (peak)

AMPLITUDEresting to max peak

WAVELENGTH

TROUGH

CHARACTERISTICS OF TRANSVERSE WAVES

Waves are described according to their

• Amplitudemeasures DISPLACEMENTsize of the disturbance

• Wavelength distance of a “repeating unit”Also called a cycle

• Velocity v speed = how fast wave travels

AMPLITUDE

– Distance between “rest & crest” or “rest & trough”

– Gives indication of “power” or “strength” of wave(magnitude of earthquake = Richter scale)

– Does not affect

velocity of wave

– Determines loudness (sound) or brightness (EM wave)

WAVELENGTH

• Distance between any two repeating points on a wave

crest-crest, trough-trough,expansion-expansion, compression-compression

• Determines what colorswe see; what notes we hear (pitch)

• Shorter wavelengths have more cycles per minute because they aren’t as long

VELOCITY v• Rate at which the energy

travels; speed & direction

• Depends on medium– Mechanical waves

travel faster through dense mediums

– EM Waves are faster through less dense mediums

FREQUENCY ƒ

• measured in wavelengths/second or cycles/second

Hertz (Hz) = number of wavelengths in 1 second

• Frequency is related to velocity: v = ƒ

How often number of wavelengths that pass any point per second

Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light in avacuum ).

At this speed they can go around the world 8 times in one second.

Speed of Electromagnetic waves

Wavelength and frequency

• Speed of light in any medium is a constant

• Speed = wavelength x frequency

• Large wavelength = low frequency• Small wavelength = high frequency

Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency

Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)

RADIO WAVES

Have the longest wavelengths and

lowest frequencies of all

the electromagnetic

waves.

Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from

several satellites to the receiver, determining the distance to each satellite.

A radio picks up radio waves through an antenna and converts it to sound waves.– Each radio station in an area broadcasts at a

different frequency. • # on radio dial tells frequency.

MRI (MAGNETIC RESONACE IMAGING)

Uses Short wave radio waves with a magnet to create an image.

MICROWAVES

Have the shortest wavelengths and

the highest frequency of the

radio waves.

Used 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.

MICROWAVES

INFRARED RAYS

Infrared= below redShorter wavelength

and higher frequency than microwaves.

INFRARED RAYS

You can feel the longest ones as warmth on your

skinWarm objects give

off more heat energy than cool

objects.

VISIBLE LIGHT

Shorter wavelength and higher frequency than

infrared rays.Electromagnetic waves we

can see.Longest wavelength= red

lightShortest wavelength=

violet (purple) light

When 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 RAYS

Shorter wavelength and higher frequency than visible light

Carry more energy than visible light

Used to kill bacteria.

(Sterilization of equipment)

Too much can cause skin cancer.

Use sun block to protect against (UV rays)

Causes your skin to produce Vitamin D (good for teeth and bones)

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.

Exploding nuclear weapons emit gamma rays.

Brief Summary

A. All electromagnetic waves travel at the same speed. (300,000,000 meters/second) in a vacuum.

B. They all have different wavelengths and different frequencies.– Long wavelength-lowest frequency– Short wavelength highest frequency– The higher the frequency the higher the

energy.

Visible spectrum

Wavelength of visible light ranges from 700nm to 400nm.

nm = nanometer (10-9 m) or 0.0000007m to 0.0000004m

Spectrophotometer

Wavelength dial

Wavelength window

Transparent• An object that lets all light pass

through it is called transparent.• These objects are transparent: clear

glass, eyeglasses, window, fish tank, clear plastics, and transparent tape.

Translucent• An object that lets some light pass

through it is called translucent.• These objects are translucent:

waxed paper, sunglasses, frosted glass, and thin fabrics.

Opaque• An object that lets no light pass

through it is called opaque.• These objects are opaque: rock,

metal, wood, fog, aluminum foil, thick paper, and brick.

Refraction

• Light interacts with transparent media and refracts or bends

• Refraction of light occurs whenever light travels from one transparent medium into another

• Light waves travel at different speeds through different media

Refraction

• Light waves travel at different speeds through different media when the light changes speeds, it bends

Refraction

Index of Refraction

• The “light slowing factor” is called the index of refraction (n)– glass has n = 1.52, meaning that light

travels about 1.5 times slower in glass than in vacuum

– water has n = 1.33– air has n = 1.00028– vacuum is n = 1.00000 (speed of light

at full capacity)

Index of Refraction

• The larger the index of refraction, the slower the speed of light in the medium

• The larger the index of refraction, the more the light bends (the bigger the difference between the angle of incidence and the angle of refraction)

Refraction at a plane surface

• Light bends at interface between two media

• Measurethe anglesfrom the normal line(N)

• I=Incidence• R=Refraction

Refraction at a plane surface

• Light bends and makesthe straw look brokenor the root beer glass look thinner than it is(when the glass is inwater, you can see howthick it really is)

Convex Lenses

Thicker in the center than edges. – Lens that converges

(brings together) light rays.

– Magnifies a flat image

Concave Lenses

• Lenses that are thicker at the edges and thinner in the center. – Diverges light rays – Reduces an image

Refraction of light through flat plastic

What the lines really look like.

What the lines look like when viewed through an acrylic semicircle placed between points A and B

Refraction of light through concave or convex lenses

What the lines really look like.

What the lines look like when viewed through an convex or concave lenses placed between points A and B

Reflections• Reflect is when light

or an image bounces back off an object’s surface.

• Light can bounce back off an opaque object.

Law of Reflection

• Light travels in straight lines• Reflection off a flat surface follows a

simple rule:– angle in (incidence) equals angle out

(reflection)– angles measured from surface “normal”

(perpendicular)

Reflection

Measure the angles from the normal linei = Angle of Incidencer = Angle of refraction

Color

Make a Splash with Color http://www.thetech.org/exhibits/online/color/overview/

What wavelength goes with which color?

http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html

Color of transparent materials

• Light passes through transparent materials

• Some transparent materials absorb certain wavelengths of light and transmit others, the color we see depends on the wavelengths that are transmitted

• The more light that is absorbed, the less light is transmitted and vice versa

Color of opaque objects

• The color an opaque object appears depends on the colors of light it absorbs and reflects.

For example, a red book only reflects red light. It absorbs all the other wavelengths of visible light.

White

light Only red light is reflected

A white hat would reflect all seven colors:

A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):

Purple light

White

light

White

light

White

light

Using colored light

• If we look at a colored object in colored light we see something different. For example:

White

light

Shorts look blue

Shirt looks red

In different colors of light things would look different:

Red

lightShirt looks red

Shorts look black(Blue shorts absorb red light)

Blue

light

Shirt looks black(Red shirt absorbs blue light

Shorts look blue

Using filters• Filters can be used to “block” out different colors of light:

Red Filter

Magenta Filter

• Torgerson, E. "Light reflect refract absorb abel." Mr. Torgerson's Science Daily      Agenda. WordPress, 2011. Web. 1 Feb. 2015.      <https://etorgerson.files.wordpress.com/2011/05/      light-reflect-refract-absorb-label.jpg>