Electromagnetic Electromagnetic Spectrum and Visible Spectrum and Visible

LightLightIn this unit:

1) Electromagnetic Spectrum2) Properties of Light3) Visible Light4) Color Addition5) Color Subtraction6) Shadows

Part 1- The Part 1- The Electromagnetic Electromagnetic

SpectrumSpectrum

The electromagnetic spectrum contains 7 different types of EM wave. The portion of the spectrum that our eyes sense is called visible light.

EM WavesEM Waves

All waves in this spectrum are transverse waves.

They are the result of fluctuating electric and magnetic fields.

Radio WavesRadio Waves

Wavelength: 1mm-100kmFrequency: <3x1011 Hzhttp://www.darvill.clara.net/emag/

emagradio.htm

MicrowavesMicrowavesWavelength Range: 1mm - 25umFrequency Range: 3x1011 – 3x1013 Hzhttp://www.darvill.clara.net/emag/emagmicro.htm

Infrared WavesInfrared WavesFrequency Range: 1x1013 - 4x1014 HzWavelength Range: 25um - 750nmhttp://www.darvill.clara.net/emag/emaginfra.htm

Visible Light WavesVisible Light Waves

Frequency Range: 4x1014 - 7.5x1014 HzWavelength Range: 750nm - 400 nmhttp://www.darvill.clara.net/emag/

emagvis.htm

Ultraviolet WavesUltraviolet Waves

Frequency Range: 1015 - 1017 HzWavelength Range: 400nm - 1nmhttp://www.darvill.clara.net/emag/

emaguv.htm

X-Ray WavesX-Ray Waves

Frequency Range: 1017 - 1020 HzWavelength Range: 1nm-0.1nmhttp://www.darvill.clara.net/emag/

emagxray.htm

Gamma WavesGamma Waves

Frequency Range: 1020 - 1024 HzWavelength Range: <0.1nmShortest wavelength and highest

frequency. http://www.darvill.clara.net/emag/

emaggamma.htm

Part 2 – Properties of Part 2 – 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.

We see things because they reflect light into our eyes:

Homework

Luminous and non-luminous objects

A luminous object is one that produces light.

A non-luminous object is one that reflects light.

Luminous objects Reflectors

Shadows

Shadows are places where light is “blocked”:

Rays of light

Properties of Light Properties of Light summarysummary

1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect

light into our eyes4) Shadows are formed when light is

blocked by an object

Part 3- Visible LightPart 3- Visible LightVisible light is the part of the EM spectrum that we

as humans can detect with our eyes. It is not a single color; it is made up of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

The colors of visible light:The colors of visible light:

RedOrangeYellowGreenBlue

IndigoViolet

Since the color a visible light wave appears is a product of the wavelength and frequency, color is a property of the wave.

Seeing ColorsSeeing ColorsColor is detected by cone cells in the

retina of the eye. There are only 3 kinds of cone cells: red,

green, and blue. Human’s see all the colors of the rainbow

by adding together different amount of red, blue, and green.

Part 4 - Color AdditionPart 4 - Color AdditionWhite light can be split up to make separate

colours. These colours can be added together again.

The primary colours of light are red, blue and green:Adding blue and

red makes magenta (purple)

Adding blue and green makes cyan

(light blue)

Adding all three makes white again

Adding red and green makes yellow

Color AdditionColor AdditionPrimary colors of light: red,

blue and greenAdd together to make all the

colors of the visible spectrum. The colors they create when

added together in full strength are called secondary colors of light: cyan, magenta, and yellow.

When all three primary colors of light are added together they create white light.

Part 5 - Color Part 5 - Color SubtractionSubtraction

White light from the sun or from a light bulb illuminates objects. White light contains ALL the colors of light.

Filters can be used to absorb out different colors of light:

Red Filter

Magenta Filter

Color SubtractionColor SubtractionObjects that contain pigments

appear colors depending on what colors of light are absorbed and what colors are reflected.

There are three primary pigments that combine to make all the other colors of pigment in the world. Cyan, Magenta, and Yellow. When they combine they create the secondary pigments red, blue and green.

What color does it What color does it appear? appear?

The color an object appears depends on the colors of light it reflects…It acts just like the filters. We can predict the color an object will appear based on color subtraction.

For example, a red book only reflects red light:

White

light

Only red light is

reflected

A white hat would reflect all three colors:

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

red and blue):

Magenta light

White

light

Using colored lightUsing colored light

If we look at a coloured object in coloured light we see something different. For example, consider a this outfit:

White

light

Shorts look blue

Shirt looks red

In different colors of light this outfit would look different:

Red

lightShirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue

Some further examples:

Object Color of lightColor object seems to be

Red socks

Red Red

Blue Black

Green Black

Blue teddy

Red Black

Blue

Green

Green camel

Red

Blue

Green

Magenta book

Red

Blue

Green

Color Subtraction with Color Subtraction with filtersfilters

Color of filter

Color absorbed Colors Reflected Color Seen

Red

Green

Blue

Cyan

Magenta

Yellow

Red and Green

Cyan and Magenta

Yellow and Green

Red

Magenta

White

Yellow

Blue Green

Cyan Black

Part 6 - ShadowsPart 6 - ShadowsWhenever light is blocked a shadow is created. If an object is near the light source the shadow

will be larger. If the object is far from the light source the

shadow will be smaller. A persons shadow will be the longest when the

sun is farthest away and is at an angle (dusk and dawn).

A person’s shadow will be the shortest at noon because the sun is as close as it can be and is directly over head.

Parts of a ShadowParts of a ShadowUmbra- The area

directly behind the object where ALL light is blocked. Appears dark black.

Penumbra- The area around the object where light is only partially blocked. Appears gray and fuzzy.

Colored ShadowsColored ShadowsWhen the primary colors of light are ADDED together white light appears. When an object is placed in front of white light from color addition it will form 7 shadows. Primary Shadows:Magenta, Cyan and YellowSecondary shadows appear where the primary shadows overlap. Secondary Shadows:Red, Blue, Green, Black

Magenta = Green is blocked, so blue and red are reflected. Cyan = Red is blocked, so blue and green are reflected. Yellow = Blue is blocked, so red and green are reflected. Red = Blue and Green are blocked, and red is reflected. Blue = Red and Green are blocked, and blue is reflected. Green = Red and Blue are blocked, and green is reflected. Black = All light is blocked!