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Preparation for Physics Final > Chapter 27 > Flashcards

Chapter 27 Flashcards

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1
Q

How long has light been studied?

A

For thousands of years.

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2
Q

What did Greek philosophers think of light?

A

That it consisted of tiny particles which could enter the eye to create the sensation of vision

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3
Q

What did Socrates and Plato think?

A

That vision resulted from streamers or filaments emitted by the eye making contact with an object.

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4
Q

Up until _________, most philosophers and scientists thought that light consisted of particles .

A

Newton

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5
Q

Who taught that light traveled in waves.

A

Empedocles and Christian Huygens

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6
Q

How was the particle theory supported?

A

By the fact that light seemed to move in straight lines instead of spreading out as waves do.

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7
Q

What evidence did Huygens provide?

A

That under some circumstances light does spread out (diffraction)

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8
Q

Who published a theory in 1905 explaning the photoelectric effect?

A

Einstein

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9
Q

Light consists of …

A

Photons

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10
Q

What are photons?

A

Massless bundles of concentrated electromagnetic energy.

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11
Q

Scientists now agree that light has a _______nature, part __________and part __________.

A

dual; particle; wave

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12
Q

It was not known whether light travels instantaneously or with finite speed until…

A

the late 1600s

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13
Q

Who tried to measure the time a light beam takes to travel to a distant miror and back?

A

Galileo

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14
Q

Why couldn’t Galileo measure the time a light beam takes to travel to a distant miror and back?

A

The time was so short that he couldn’t begin to measure it.

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15
Q

What happened to the people who tried to measure the time a light beam takes to travel to a distant miror and back?

A

They succeeded in measuring their own reaction times

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16
Q

Who supplied the first demonstration that light travels at a finite speed?f

A

Danism astronomer Olaus Roemer, 1675

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17
Q

What did Roemer do first?

A

He made very careful measurements of the periods of Jupiter’s moons.

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18
Q

What is the innermost moon of jupiter called?

A

Io

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19
Q

How long does it take Io to revolve around Jupiter?

A

42.5 hours

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20
Q

How could Roemer be sure that his measurements were accurate?

A

Bc Io disappears periodically into Jupiters shadow

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21
Q

What irregularities did Roemer find?

A

While Earth wasmoving away from Jupiter, from position B to C, the measured periods of Io were all somewhat longer than average. When Earth was moving toward Jupiter, from E to F, the measured periods were shorter than average.

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22
Q

What did Roemer estimate about the cumulative discrepancy between A and D?

A

The cumulative discrepancy between A and D amounted to about 22 minutes, when Earth was at position D, Io would pass into Jupiter’s shadow 22 minutes late, compared with observations at position A.

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23
Q

What did Christian Huygens interpret about the discrepancy?

A

When Earth was farther away from Jupiter, it was the light that was late, not the moon.

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24
Q

Io passed into Jupiter’s _________at the predicted time, but the _______carrying the message did not reach Roemer until it had traveled the extra distance across the diamter of _________ ________.

A

shadow; light; Earth’s orbit

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25
Q

What is the speed of light?

A

300,000km/s

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26
Q

Who performed the most famous experiment measuring the speed of light.

A

Albert Michaelson, American physicist

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27
Q

What was Michaelson’s experiment?

A

An octagonal mirror was adjusted so that a beam of light was reflected to a stationary mirror located on a mountain 35 km away and then reflected back to the octagonal mirror into the eye of an abserver. The distance the light had to travel to the distant mountain was known, so Michaelson had to find only the time it took to make a round trip. When the mirror was spun, short bursts of light reached the mountain mirror and were reflected back to the spinning octagonal mirror. If the rotation mirror made exactly 1/8 rotation in the time the light the trip to the distant mountain and back, the mirror was in a position to reflect the light to the observer. If the mirror was rotated too slowly or too quickly, it would not be in a position to relfect light. When the light entered the eyepiece, Michelson knew octagonal mirror to make 1/8 of a rotation was the same. He divided the 70-km round trip distance by this time.

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28
Q

What was Michelson’s experimental value for the speed of light?

A

299,920 km/s

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29
Q

When did Michelson recieve the Nobel Prize in physics?

A

In 1907, he was the first American scientist to receive it.

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30
Q

Is the speed of light universal in a vacuum?

A

Yes

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31
Q

How many trips could light make in 1 second?

A

7.5

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32
Q

How long does it take light to travel from the sun and Earth?

A

8 minutes

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33
Q

How long does it take light for light to reach the next nearest star, Alpha Centauri?

A

4 years

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34
Q

The distance light travels in one year is called…

A

A light-year

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35
Q

Light is energy that is emitted by…

A

accelerating electric charges - often electrons in atoms

36
Q

Electromagnetic Wave

A

This energy travels in a wave that is partly electric and partly magnetic

37
Q

Electromagnetic spectrum

A

The range of electromagnetic waves

38
Q

How does the lowest frequency of light we can see appear?

A

Red

39
Q

How does the highest frequency of light we can see appear?

A

Violet

40
Q

How do the highest frequency compare to the lowest frequency?

A

nearly twice the frequency.

41
Q

What are electromagnetic waves of frequencies lower than the red of visible light called?

A

Infrared

42
Q

What are electromagnetic waves of frequencies higher than the violet of visible light called?

A

Ultraviolet

43
Q

How is light carried?

A

Light is energy carried in an electromagnetic wave that is generated by vibrating electric charges.

44
Q

What happens when light strikes matter?

A

Electron in the matter are forced into vibration. In effect, vibration in an emitter are transferred to vibrations in a receiver.

45
Q

What does exactly how a receiving material responds when light is incident upon depend on?

A

The frequency of the light and the natural frequency of electrons in the material.

46
Q

Visible light vibrates at a very high rate. T or F?

A

True, more than 100 trillion times per second

47
Q

If a charged objected is to repond to these ultrafast vibrations…

A

Then it must have very little inertia

48
Q

Light passes through materials whose ______absorb the ________ and immediately reemit it as light.

A

atoms; energy

49
Q

Materials that transmit light are called…

A

transparent

50
Q

What type of materials respond more to vibrations at some frequencies more than others?

A

Springy (elastic)

51
Q

The natural vibration frequencies or an electron depend on…

A

How strongly it is attached to a nearby nucleus

52
Q

What type of range do electrons’s natural vibration frequency in glass have?

A

Ultraviolet

53
Q

What happens when ultraviolet light shines on glass?

A

Resonance occurs as the wave builds and maintains a large vibration between the electron and the atomic nucleus, just as a large vibration is built when pushing someone at the resonant frequency in a swing.

54
Q

The energy received by the atom can be either passed on to neighboring atoms by…

A

collisions or remitted as light

55
Q

When the electromagnetic wave has a lower frequency than ultraviolet, as visible light doesm what happens to the electrons? Atoms?

A

The electons are forced into vibration with smaller amplitudes. The energy of the vibrating electron is reemited as light. The atom holds the energy for less time, with less chance of collison with neighboring stoms, and less energy is transferred as heat.

56
Q

Is glass transparent to all the frequencies of vivible light?

A

Yes.

57
Q

The frequency of the reemitted light passed from atom to atom is identical to that of the….

A

light that produced the vibration to begin with.

58
Q

What is the result of a slight time delay between absorption and reemission?

A

A lower average of light through a transparent material.

59
Q

Light travels at different average speeds through…

A

different materials

60
Q

In water, light travels at about ______of its speed in a vacuum .

A

75%/0.75c

61
Q

In glass, light travels at about ______, depending on the type of glass.

A

0.67c

62
Q

In a diamond, light travels at _______.

A

0.40c

63
Q

When light emerged from the materials into the air, it travels at…

A

the original speed of light

64
Q

Infrared waves vibrate the electrons, but also…

A

the entire structure of the glass.

65
Q

The vibration of the structure increases…

A

The internal energy of the glass and makes it warmer.

66
Q

Opaque

A

Materials that absorb light with out the reemission and thus allow no light through them

67
Q

In opaque materials, any __________ _________given by light to the atoms and molecules are turned into random _________ ________ that is, into internal energy/

A

coordinated vibrations; kinetic energy

68
Q

Are metals opaque?

A

Yes

69
Q

In metals, the outer electrons of atoms…

A

Are not bound to any particular atom; They are free to wander with very little restraint throughout the material. This why they conduct heat and electricity well.

70
Q

Why is metal shiny?

A

When light shines on metal and sets these free electrons into vibration, their energy does not spring from atom to atom in the material but is reemitted as visible light. This remitted as a reflection.

71
Q

Our atmosphere is trnasparent to visible light and some infrared, but is almost opaque to…

A

high-frequency ultraviolet waves

72
Q

Are clouds completely transparent?

A

No, they are semitransparent

73
Q

Ray

A

A thin beam of light

74
Q

Can any beam of light be thought of as made of a bundle of rays.

A

Yes

75
Q

When light shines on an object, some of the rays may be __________while others ______on in a ________-______path

A

stopped; pass; straight-line

76
Q

Shadow

A

Formed where light rays cannot reach

77
Q

How are sharp shadows produced?

A

By a small light source nearby or by a larger source farther away.

78
Q

Umbra

A

A total shadow

79
Q

Penumbra

A

A partial shadow. Appears where some of the light is blocked and light from another source fills in.

80
Q

Examples of a penumbra:

A
  • When a moon passes between Earth and the sun (solar eclipse)
81
Q

What is another occurence where shadows occur?

A

Light is bent in passing through a transparent material such as water.

82
Q

Does light travel at slightly different speeds in warm and in cold water?

A

Yes

83
Q

A single vibrating electon emits…

A

An electromagnetic wave that is polarized

84
Q

Light will pass through a pair of polarizing filters when…

A

Their polarization axes are aligned but not when they are crossed at right angles

85
Q

Light that reflects at glancing angles from ___________surfaces, such as glass, water, or roads, vibrates mainly in the ________of the _________surfaces.

A

nonmetallic; plane; reflecting

Preparation for Physics Final (11 decks)

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