Physical ScienceLight and Color

Lincoln High School

Mr. Lowery

Earth Science

2007-2008

Light and sound are both vibrations that move as waves.

Light travels a million times faster than sound

The speed of light in a vacuum is 300,000 km / sec

Light does not need a medium to travel through like sound does, it can travel through a vacuum, such as space

These waves carry energy. Vibrating electric and magnetic fields support each other and make up an electromagnetic wave

The classification of electromagnetic waves by frequency is the electromagnetic spectrum. A narrow band of this spectrum makes up the frequencies and wavelengths we can detect with our eyes as visible light.

Different frequencies result in different wavelengths. Low frequencies produce long wavelengths and high frequencies produce short ones

Why do things appear the color that they do?

• The colors we see depends on the wavelength of light. The longer the wavelength of visible light, the more red the color appears

The shorter the w of visible light, the more toward the blue end of the spectrum.

White light has all the colors of the spectrum in it.

How do we know this?

Because if we put white light through a prism, which separates light into all of the wavelengths that makes it up.

• So if white light has all the colors in it, why does a red shirt appear red?

• The dye in the shirt is of a formula to absorb all the colors BUT red, and reflect the red. The red wavelengths are reflected, and our eyes only see that wavelength

• Why does a white table top appear white?

• All of the colors are reflected, so we see that whole spectrum again. It absorbs none of the colors

• Why does the black benchtop appear black?

• It absorbs all of the colors, reflects none, so we don’t see anything. Black isnt a color, black is the ABSENCE of all color. Our eyes are not picking up any wavelengths from that object

• Why is the sky blue?

• B/c blue wavelengths of light scatter more than longer wavelengths. Sunlight is coming at us from a fixed spot with all the w of light. The more certain w’s scatter, they come at us from different directions

• So, blue comes at us from the most directions. Our eye perceives the most dominant signal it is getting – the blue that seems to come from everywhere.

• Why are sunsets red, and redder than the noon sun?

• Still a scattering issue. The noon sun overhead allows for the reds that only scatter a little, oranges that scatter a bit more, yellows that scatter even more and comes at us from more directions than the reds

• At sunset, the sun is really low in the horizon. The red rays that are very direct are now the dominant ones. The yellows and orange are not as dominant b/c some of them scattered but are not picked up by the eye.