Light and Light and Electromagnetic Waves &Electromagnetic Waves &

the Electromagnetic the Electromagnetic SpectrumSpectrum

Light and the EyeLight and the Eye

NATURE OF WAVESNATURE OF WAVES

Waves (Def.) – A wave is a disturbance that transfers energy through vibrations.

Medium/Matter – Substance or region through which a wave is transmitted.

Speed of Waves – Depends on the properties of the medium.

© 2000 Microsoft Clip Gallery

Part 1 – Properties of Part 1 – Properties of LightLight

Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

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

Light travels much faster than sound. For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

http://studyjams.scholastic.com/studyjams/jams/science/energy-light-sound/light.htm

Properties of LightProperties of Light

When light strikes an object it is:1) Reflected2) Transmitted 3) Absorbed

Properties of LightProperties of Light

Color of objects is the color it reflects– Ex- an orange is orange because it

absorbs every color BUT orange, instead it reflects orange

– If you do not shine orange light on it, it will appear black

– Black is the absence of color, white is the blending of all colors

Properties of LightProperties of Light

Reflection- when an object or wave bounces back off a surface

Properties of LightProperties of Light

Reflection- when an object or wave bounces back off a surface

Law of reflection- angle made from incoming wave = the angle made from reflected wave

Properties of LightProperties of Light

Refraction- bending of light waves due to a change in speed

LIGHT: Refraction LIGHT: Refraction of Lightof Light

Refraction – Bending of light due to a change in speed.

– Index of Refraction – Amount by which a material refracts light.

– Prisms – Glass that bends light. Different frequencies are bent different amounts & light is broken out into different colors.

Properties of LightProperties of Light

Refraction- bending of light waves due to a change in speed

Lens- curved glass or transparent material that refracts light

Convex lens- thicker in the center than the edges (bends light in)

http://studyjams.scholastic.com/studyjams/jams/science/energy-light-sound/light-absorb-reflect-refract.htm

PowerPoint created by Mrs. B-D 2007

Light, Lens, Action!Light, Lens, Action!From the moment you wake

up in the morning to the time you go to sleep at night, your eyes are acting like a video camera. Everything you look at is then sent to your brain for processing and storage much like a video. This is a very simplified explanation, but as you read on, you will discover why the sense of sight is actually considered the most complex of the five senses.

PowerPoint created by Mrs. B-D 2007

How the Eye WorksHow the Eye Works

Take a moment to locate an object around you. Do you know how you are able to see it? Would you believe that what you are actually seeing are beams of light bouncing off of the object and into your eyes? It is hard to believe, but it is true.

The light rays enter the eye through the cornea, which is a thick, transparent protective layer on the surface of your eye. Then the light rays pass through the pupil (the dark circle in the center of your eye) and into the lens.

PowerPoint created by Mrs. B-D 2007

How the Eye Works How the Eye Works continuedcontinued

Your lens in your eyes change size all the time. When you look at objects real close up, the lens gets thicker. If you look at objects far away, it gets thinner. It does this to help you focus the correct image on the retina.

After light passes through the lens it shines through the back of the eye where it hits the retina. The retina takes the light and changes it into nerve impulse so the brain can understand what the eye sees. It sends the message to the brain by way of the optic nerve.

PowerPoint created by Mrs. B-D 2007

Parts of the EyeParts of the Eye

PowerPoint created by Mrs. B-D 2007

• CorneaCornea: : The cornea is a clear white The cornea is a clear white covering over the outside of the eye. covering over the outside of the eye. It helps the eye focus like a lens on a It helps the eye focus like a lens on a camera.camera.

• IrisIris: : The iris is the part of your eye The iris is the part of your eye that has color. It gets bigger and that has color. It gets bigger and smaller to let in different amounts of smaller to let in different amounts of light.light.

• PupilPupil: : Black opening in the middle of Black opening in the middle of the eye. Light comes through this the eye. Light comes through this opening.opening.

PowerPoint created by Mrs. B-D 2007

• LensLens: The lens bends light. This helps : The lens bends light. This helps the eye see close up and far away the eye see close up and far away things.things.

• RetinaRetina: The retina has nerve cells : The retina has nerve cells called rods and cones that detect called rods and cones that detect light. It is in the back of your eye.light. It is in the back of your eye.

• Optic NerveOptic Nerve: The optic nerve carries : The optic nerve carries electrical signals from your retina to electrical signals from your retina to your brain so you can see. your brain so you can see.

PowerPoint created by Mrs. B-D 2007

Rods and ConesRods and Cones Rods and cones are special

cells that process light. Rods and cones are

extremely small. In fact, there are about 120 million rods and 7 million cones in each eye!

Rods help us see black and white and shades of grey.

Cones help us see color. You have three kinds of cones are - red, green, and blue. These cones work together to help us see millions of colors.

PowerPoint created by Mrs. B-D 2007

Flipped Image Flipped Image

When you see images, they turn upside down when they hit the retina. So your brain sees everything in the world upside down. Your brain basically flips everything around so it is right side up again.

Electromagnetic Electromagnetic SpectrumSpectrum

Electromagnetic WavesElectromagnetic Waves• Transverse waves without a

medium! • (They can travel through empty

space)

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

electrical properties to them.

When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.

RESULT-An electromagnetic wave.

Waves or Particles?• Electromagnetic radiation has properties of

waves but also can be thought of as a stream of particles.

– Example: Light• Light as a wave: Light behaves as a

transverse wave which we can filter using polarized lenses.

• Light as particles (photons): When directed at a substance light can knock electrons off of a substance (Photoelectric effect)

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

MICROWAVES

INFRARED RAYS

VISIBLE LIGHT

ULTRAVIOLET RAYS

X-RAYS

GAMMA RAYS

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

Rays)

RADIO WAVESRADIO 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.

MICROWAVESMICROWAVES

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.

RADAR (Radio Detection and Ranging)• Used to find the

speed of an object by sending out radio waves and measuring the time it takes them to return.

INFRARED RAYSINFRARED RAYS

Infrared= below redShorter

wavelength and higher frequency

than microwaves.

You can feel the longest

ones as warmth on your skin

Warm objects give off more

heat energy than cool objects.

Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given

off. Therefore people give

off infrared rays.

Heat lamps give off infrared waves.

VISIBLE LIGHTVISIBLE LIGHTShorter wavelength and

higher frequency than infrared rays.

Electromagnetic waves we can see.

Longest wavelength= red light

Shortest 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 RAYSULTRAVIOLET 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- RAYSX- RAYSShorter

wavelength and higher

frequency than UV-rays

Carry 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 RAYSGAMMA 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.

The Incredible Hulk was the

victim of gamma

radiation.

Exploding nuclear

weapons emit

gamma rays.

Brief SUMMARYA. 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.