Exam 3- Ch 1. Our World of Light and Color

7 regions of electromagnetic spectrum

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Wavelength

Distance between successive waves; the wavelength of light generally determines its color

Three projectors are adjusted to produce white light on a screen. If you stand in front of the red projector, what color will your shadow be? If you stand in front of the green projector, what color will your shadow be? If you stand in front of the blue projector, what color will your shadow be?

All three colors combined create white light. When you block the red light, you are left with cyan light (blue plus green). When you block the green light, you are left with magenta light (blue plus red). When you block the blue light, you are left with yellow light (green plus red).

Is it possible to produce black by shining the right mixture of colored lights on a white screen?

It is not possible to produce black by shining light on a white screen. Black is the absence of color rather than a color itself. To create black on a white screen, you must eliminate all light shining on a white screen to achieve black.

How are rainbows formed?

Natural rainbows arise from light that is reflected in raindrops. Light enters the spherical drop of water, is reflected inside of the drop, and emerges at a 42 degree angle.

Wavelength of 7 regions of electromagnetic spectrum

Radio: 10 ^2 to 10^-1 m Microwave: 10^-1 to 10^-3 m Infrared: 10^-3 to 7 x10^-7 m Visible: 7 x10^-7 to 4 x10^-7 m Ultraviolet: 4 x10^-7 to 10 ^-9 m X-rays: 10 ^-9 to 10 ^-11 m Gamma: 10 ^-11 to 10 ^-13 m

Why is the sky blue?

TA HW Solution-The sky is blue because light entering the atmosphere scatters off of the air molecules. Blue light scatters a lot better than any other wavelength of light, causing it to be the dominant color. Internet-The air molecules scatter blue light better than red light, so more blue light reaches our eyes.

Why are sunsets red?

TA HW Solution: As the sun sets, it goes through more air as it travels to our eyes. Since most of the blue light has already been scattered, the remaining colors (yellow, orange, red, etc.) are the only colors remain. This gives rise to the colors seen during a sunset. Internet: Rayleigh Scattering- By the time a beam of light gets to the ground at sunset, all of the high-frequency light has already been scattered. Only the lower frequencies remain, resulting in a red sunset.

Dispersion

The separation of visible light into its different colors

What is the range of wavelengths in the visible spectrum expressed in nanometers and expressed in meters?

Visible light ranges from blue light (shortest wavelength) to red light (longest wave- length). The shortest wavelength of visible light is about 400 nm (4 ˆ 10 ́7 m) and the longest wavelength of visible light is about 700 nm (7 ˆ 10 ́7 m).

What is a nanometer?

A nanometer is a unit of measure that is used for exceptionally small things. An atom is about 10 nanometers across. The wavelength of visible light is a few hundred nanometers. A nanometer represents a billionth of a meter. This is written as 1 nm = 10 ́9 m.

Suppose we lived in a world in which the atmosphere consisted of particles that scattered orange and red light more effectively than blue light. What color would the setting sun be in such a world?

The setting sun's colors represent the colors remaining after the light that is scattered most easily has been eliminated. In the real world, this is blue light, so the setting sun has yellows, oranges and reds. In this fantasy world, orange and red light is scattered most easily. This means the light remaining would be the blue and green lights. This would mean the setting sun is going to be green at first and blue as the sun reaches the horizon much like the sun starts as orange and becomes red as the sun reaches the horizon.

Four-color printing uses magenta, yellow, cyan, and black inks. Which of these colors would be combined to print red on a white page?

To achieve red, we need to subtract away the green light and the blue light. Minus green dye is magenta and minus blue is yellow. This means we would need magenta and yellow ink to print the color red.

Why must you look in the direction of your shadow in order to observe a rainbow?

White light enters a raindrop and reflects twice and emerges in the direction from which it came. During this time, dispersion causes the color separation that we see. Since the light is emerging in the direction from which it came, to see a rainbow, we must look in the direction of our shadow.