# Electromagnetic Spectrum and Visible Light

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Electromagnetic Spectrum and Visible Light
In this unit: Electromagnetic Spectrum Properties of Light Visible Light Color Addition Color Subtraction Shadows

Part 1- The Electromagnetic Spectrum
The electromagnetic spectrum contains 7 different types of EM wave. The portion of the spectrum that our eyes sense is called visible light.

EM Waves All waves in this spectrum are transverse waves. They are the result of fluctuating electric and magnetic fields.

Radio Waves Wavelength: 1mm-100km Frequency: <3x1011 Hz

Microwaves Wavelength Range: 1mm - 25um Frequency Range: 3x1011 – 3x1013 Hz

Infrared Waves Frequency Range: 1x x1014 Hz Wavelength Range: 25um - 750nm

Visible Light Waves Frequency Range: 4x x1014 Hz Wavelength Range: 750nm nm

Ultraviolet Waves Frequency Range: Hz Wavelength Range: 400nm - 1nm

X-Ray Waves Frequency Range: Hz Wavelength Range: 1nm-0.1nm

Gamma Waves Frequency Range: Hz Wavelength Range: <0.1nm Shortest wavelength and highest frequency.

Part 2 – Properties of Light
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:
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

Properties of Light summary
Light travels in straight lines Light travels much faster than sound We see things because they reflect light into our eyes Shadows are formed when light is blocked by an object

Part 3- Visible Light Visible 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:
Red Orange Yellow Green Blue Indigo Violet Since the color a visible light wave appears is a product of the wavelength and frequency, color is a property of the wave.

Seeing Colors Color 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 Addition White 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 red and green makes yellow Adding all three makes white again

Color Addition Primary colors of light: red, blue and green Add 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 Subtraction
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 Subtraction Objects 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 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: Homework White light Only red light is reflected

A white hat would reflect all seven colors:
A pair of purple trousers would reflect magenta light (and red and blue, as magenta is made up of red and blue): Magenta light A white hat would reflect all seven colors: White light

Using colored light If we look at a coloured object in coloured light we see something different. For example, consider a this outfit: Shirt looks red White light Shorts look blue

In different colors of light this outfit would look different:
Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue

Some further examples:
Object Color of light Color object seems to be Red socks Red Blue Black Green Blue teddy Green camel Magenta book Homework

Color Subtraction with filters
Color of filter Color absorbed Colors Reflected Color Seen Red Green Blue Cyan Magenta Yellow Red and Green Cyan and Magenta Yellow and Green Color of filter

Red Blue Green White Yellow Cyan Magenta Black

Part 6 - Shadows Whenever 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 Shadow Umbra- 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 Shadows When 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 Yellow Secondary 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!