Physics 100
Test Review Answers: Light
1. Light: electromagnetic radiation with wavelengths between 400 and 700 nanometers
2. Particle-like characteristics of light:
a. It’s made up of particles, called “photons.”
b. Light has momentum
c. Light is pulled by gravity
d. Light can travel in a vacuum
3. Wave-like characteristics of light:
a. Light is an oscillation that travels through space.
b. Light has a measureable wavelength, frequency, period, etc.
c. Light exhibits other wave properties, such as refraction, reflection, and scattering
4. Red, orange, yellow, green, blue, indigo, violet
5. Radio, Microwave, Infrared
6. Ultravioliet, X-rays, Gamma Rays
7. Long-wavelength end = “red end.” Short wavelength end = “blue end”
8. Shorter wavelengths bend more sharply.
9.
10. Stare at a picture made up of a few vivid colors. Keep your head still while you stare. Then look at a
bright white sheet of paper. When you look at the white paper, you will see colors. You see the new
colors because your eyes’ color receptors got tired of seeing the first colors. The colors that you see when
you look at white light are what you get if you remove the first colors from the rainbow that makes up
white light.
11. Short wavelengths are generally more dangerous, because they have the most energy.
12. Blue = hottest; Red = coolest
13.
14. 670,000,000mph. That will be the answer no matter which way you’re going or how fast you’re moving.
15. Light is fast, but it does take time for light to get from one place to another. When you see a star, you are
seeing light that left that star at some time in the past.
16. When photons of light travel through a substance, no single photon makes the entire journey. When a
photon hits a molecule, the molecule absorbs the photon and its energy. A moment later, the molecule
re-emits another photon, which travels until it hits the next molecule. These “pit stops” at each molecule
take time. So, while Light’s speed between molecules is constant, the time it takes for photons to be reemitted slows light down when it travels through more dense substances.
17. The index of refraction of a substance is inversely proportional to the speed of light through that
substance. Higher index, lower speed.
18. You know the angle of refraction is greater than 35 degrees. [It’s passing from a material through which
light travels slowly (high index of refraction) to a material through which light travels fast. If light is a car,
the wheel that hits the new material first will speed up, causing the car to turn in such a way that the
angle of refraction is greater than the angle of incidence.]
19. Aim below where you see the fish.
20. Blue wavelengths are scattered by our atmosphere. The get scattered throughout the sky, so no matter
where you look, you see blue.
21. Dawn and dusk are the times of day when the sun’s rays travel through the greatest thickness of
atmosphere. The longest wavelengths of visible light (red) are best able to penetrate that greater
thickness of atmosphere.
22.
23.
24. The flatter ones have longer focal lengths.
25.
26.
27.
28.