Notes: the Electromagnetic Spectrum and the Eye

NOTES: THE ELECTROMAGNETIC SPECTRUM AND THE EYE

Performance Indicator: 8.P.3A.5

Construct explanations for how humans see color as a result of the transmission, absorption, and reflection of light waves by various materials.

We only see the rainbow of light waves called ______. In the visible spectrum of light, the color of the light depends on the frequency. The order of colors from longest to shortest wavelength is red, orange, yellow, green, blue, indigo, and violet (ROY G. BIV).

HOW WE SEE LIGHT AND COLORS

What we are seeing when we see an object is reflected light.

When we see an object of a certain color that means that ______of that color's ______is being ______off the object. When you see a red shirt, the shirt is absorbing all the colors of light except for the red color. The frequency of light that we see as red is being reflected and we see that shirt as red.

ABSORPTION

• As we have learned before, most objects absorb some of the frequencies of the spectrum but reflect other frequencies.

• If a material ______a certain frequency of light, that frequency will ______be ______so its color will not be seen by the observer.

LIGHT WAVES

• The absorption and reflection of light waves by various materials results in human perception of color as follows:

• Most materials absorb light of some frequencies and reflect the rest.

ABSORPTION & REFLECTION

• If a material ______a certain frequency of light, that frequency will not be reflected, so its color will ______be perceived by the observer.

•

• If the material does not absorb a certain frequency of light, that frequency will be ______, so its color will be perceived by the observer.

REFLECTION

• The frequency that is ______makes the color for that object.

• Red apples are red because the apple’s skin does not absorb the red frequency.

BLACK OR WHITE

• When objects reflect all frequencies, the color will appear ______.

• When objects absorb all frequencies, the color will appear ______.

PRIMARY COLORS

• The human eye can distinguish thousands of different colors.

• There are 3 primary colors…

– RED, BLUE, & GREEN

• Light of almost any color can be made from mixing different amounts of the primary colors.

WHAT DO COLOR THAT WE SEE DEPEND ON:

• The colors that we see depend on 2 things.

(1) the color of light that is shined on the object and
(2) the color of light that is reflected by the object.

For example: if an object reflects red wavelengths and absorbs all others, the object will appear red in color.

COLOR FILTERS

Color filters allow only certain colors of light to pass/transmit through them; they absorb or reflect all other colors. For example, a blue filter only transmits blue light. Objects seen through a blue filter will look blue if the objects reflect blue; objects of other colors will appear black because the other color wavelengths are being absorbed by the filter.

The interaction between the eye and light emitted or reflected by an object allows sight to occur as follows:

HOW DOES THE EYE WORK?

○ _LIGHT WAVES that have been emitted or ______by an object, enter the eye and first pass through the transparent layer called the ______where they are ______.

○ The light passes by the ______ (colored part) and through the ______ which can expand and shrink to control the amount of light that gets into the eye.

○ The light rays are then refracted again as they pass through the transparent ______ (convex).

○ The lens focuses the light waves on the ______, located on the back of the inside of the eye.

○ The retina is composed of tiny light sensitive nerves that transfer the energy of the light waves to nerve impulses transmitted through the ______ to the ______for interpretation as sight.

WHAT IS THE PATHWAY LIGHT TRAVELS THROUGH THE EYE?

Some Sight Defects (Long Sight vs Short Sight)

People who are long-sighted are unable to focus on near objects. The condition is caused by the eyeball being too short, so that light rays are focused behind the retina at the back of the eye and the image is blurry. Long-sightedness is corrected using a convex (outward facing) lens. Convex lens bends light rays inwards.

Short sightedness, where the eyeball may be too long, causes problems with focusing on distant objects. They appear blurred because light from objects is focused in front of the retina. Short-sightedness is corrected using a concave (curved inwards) lens, which is placed in front of a myopic eye, moving the image back to the retina and making it clearer. Concave lens diverge/bend rays outwards.