Chapter 27 Light

Question 1

a. What is a photon?
b. Which theory of light is the photon more consistent with—the wave theory or the particle theory?

Answer 1

a. Particle of light
b. Particle theory

Question 2

How long does it take for light to travel across the diameter of Earth’s orbit around the sun?

Answer 2

About 1000 s

Question 3

How did a spinning octagonal mirror help Michelson calculate the time that light took to make the round trip to the distant
mountain?

Answer 3

He knew the spin rate of the
rotating mirror.

Question 4

How long does light take to travel from the sun to Earth? From the star Alpha Centauri to Earth?

Answer 4

About 8 min and about 4 yr

Question 5

How long does light take to travel a distance of one light-year?

Answer 5

1 yr

Question 6

What is the source of electromagnetic waves?

Answer 6

Accelerating electric charges

Question 7

Is light simply a small segment of the electromagnetic spectrum? Defend your answer.

Answer 7

Yes; the spectrum is also
made up of radio waves, IR,
UV, X-rays, and gamma rays.

Question 8

How do the frequencies of infrared and ultraviolet light compare

Answer 8

The lowest frequency is infrared, which is followed by visible light, and ultraviolet, which has the highest frequency, so there is and increase from IR to UV

Question 9

How does the role of inertia relate to the rate at which electric charges can be forced into vibration?

Answer 9

Low inertia permits rapid
vibration.

Question 10

Different bells and tuning forks have their own natural vibrations and emit their own tones when struck. How is this analogous to atoms, molecules, and light?

Answer 10

Vibrating electrons in atoms
and molecules emit light.

Question 11

Light incident upon a pane of glass slows down in passing through the glass. Does it emerge at a slower speed or at its initial
speed? Explain.

Answer 11

Initial speed; no absorption–
emission delays outside

Question 12

Will glass be transparent to light with frequencies that match its own natural frequencies?

Answer 12

No, energy is absorbed and
converted to heat.

Question 13

Does the time delay between the absorption and reemission of light affect the average speed of light in a material? Explain.

Answer 13

Yes; smaller delays, higher
average speed

Question 14

When light encounters a material, it can build up vibrations in the electrons of certain atoms that may be intense enough to last over a long period of time. Will the energy of these vibrations tend to be absorbed and turned into heat or absorbed and reemitted as light?

Answer 14

Absorbed and turned into
heat

Question 15

Why would you expect the speed of light to be slightly less in the atmosphere than in a vacuum?

Answer 15

There are interaction delays in
the atmosphere.

Question 16

What happens to the energy of light when it encounters an opaque material?

Answer 16

Turns into thermal energy

Question 17

Why are metals shiny in appearance?

Answer 17

Metals have free electrons
that vibrate, stop, and reemit
light.

Question 18

Distinguish between an umbra and a penumbra.

Answer 18

Umbra—total shadow;
penumbra—partial shadow

Question 19

a. Distinguish between a solar eclipse and a
lunar eclipse.
b. Which type of eclipse is dangerous to
your eyes if viewed directly?

Answer 19

a. Solar—moon shadow on
Earth; lunar—Earth shadow
on the moon
b. Solar

Question 20

What is the difference between light that is polarized and light that is not?

Answer 20

Polarized—vibrations occur
in one plane; non-polarized—
vibrations occur in all planes.

Question 21

Why is light from a common lamp or from a candle flame non-polarized?

Answer 21

Electrons vibrate randomly, so
light alignment is random.

Question 22

In what direction is the polarization of the glare that reflects from a horizontal surface?

Answer 22

Horizontal

Question 23

How do polarizing filters allow each eye to see separate images in the projection of three-dimensional slides or movies?

Answer 23

The Polaroid pairs in the
projector and the glasses are
at right angles.