Deck 13: Light

Question 1

Light passing from air into a denser transparent medium will

A) speed up.
B) slow down.
C) not change speed.
D) Not enough information is given to determine.

Answer 1

slow down.

Question 2

Impedance mismatches between surfaces lead to

A) constructive interference.
B) destructive interference.
C) reflection.
D) refraction.

Answer 2

reflection.

Question 3

Which answer has the colors in order from the shortest wavelength to the longest?

A) Red Green Blue
B) Red Blue Green
C) Blue Red Green
D) Blue Green Red

Answer 3

Blue Green Red

Question 4

Which answer has the colors in order from the lowest energy to the highest?

A) Red Green Blue
B) Red Blue Green
C) Blue Red Green
D) Blue Green Red

Question 5

Which answer has the colors in order from the lowest frequency to the highest?

A) Red Blue Green
B) Blue Red Green
C) Blue Green Red
D) Red Green Blue

Question 6

Light travels at about 300 million meters per second, and the Sun is about 150 million kilometers from the Earth. How long does it take light from the Sun to reach Earth?

A) 0.5 seconds
B) 2 seconds
C) 8 minutes
D) 80 minutes

Question 7

What effect causes the sky to appear blue?

A) Rayleigh scattering
B) Dispersion
C) Impedance mismatch
D) Destructive Interference

Question 8

When a narrow laser beam passes through a fine wire mesh before arriving at the wall, it forms a complicated pattern of bright spots on the wall. This pattern of spots would not occur if you sent a flashlight beam through the mesh because light from the flashlight

A) is neither coherent nor monochromatic.
B) cannot be sent through a single opening of the mesh.
C) is horizontally polarized, while laser light is vertically polarized.
D) is vertically polarized, while laser light is horizontally polarized.

Question 9

What effect causes rainbows?

A) Rayleigh scattering
B) Dispersion and total internal reflection
C) Impedance mismatch
D) Destructive Interference

Question 10

Soap bubbles have their beautiful colors when illuminated with white light because

A) of dispersion.
B) the light interferes within the bubble.
C) the light rays reflecting off the top and bottom surfaces interfere.
D) light rays reflecting off the bottom mix and interfere with each other.

Question 11

Suppose a soap bubble is illuminated with light having only wavelength (one pure color). The bubble will appear

A) to have bright and dark regions of just the one color.
B) to have multicolored regions.
C) completely invisible.
D) to behave like a mirror

Question 12

You are standing at the shore of a calm lake, trying to look beneath its surface. All you see is a strong reflection of the sky overhead. But when you put on polarizing sunglasses, the glare almost disappears and you can see fish swimming under the surface of the water. If you turn your head sideways, so that the sunglass lenses are rotated 90 $\degree$ from before, the glare will

A) become even dimmer but the fish will disappear altogether so that it is not an improvement.
B) reappear.
C) become even dimmer but the fish will also become dimmer so that it's not an improvement.
D) remain almost absent.

Question 13

Ultraviolet light causes damage to your skin while infrared light does not because

A) ultraviolet light has a longer wavelength than infrared light.
B) ultraviolet light has more photons than infrared light.
C) a photon of ultraviolet light carries much more energy than a photon of infrared light.
D) ultraviolet light is more intense than infrared light.

Question 14

Although salt crystals are clear, a pile of salt appears to be white. This is because

A) small salt grains can absorb black light, leaving only white light to be reflected.
B) some light is reflected whenever light moves from a salt granule to air or vice versa. The randomly oriented granules reflect light in all directions.
C) small salt grains are more dense than large salt crystals, and they fluoresce white light when exposed to infrared radiation.
D) small salt grains are metallic and act as mirrors, scattering light in all directions.

Question 15

The colors that you see when sunlight strikes a cut crystal wineglass or a cut diamond are a result of the fact that two light waves with

A) different wavelengths travel at different speeds in most materials.
B) the same wavelength in air can have different frequencies in a material.
C) the same frequency in air can have different wavelengths in a material.
D) the same wavelengths can have different colors.

Question 16

Suppose you live near a thermometer factory and you are suing them in court for pollution during one of their spills, where mercury droplets were detected in the air. A witness makes the statement "Yes, I know there was a lot of mercury droplets in the air because there was a rainbow in the air, just like when a rainbow forms with water droplets." Knowing that mercury is a metal and assuming there were really a lot of small mercury droplets suspended in the air please comment on the scientific validity of the statement made by the witness.

Question 17

Vegetable oil and Pyrex glass have almost exactly the same indices of refraction-the speed of light is the same in both materials. If you submerge a clear Pyrex dish in vegetable oil,

A) the Pyrex dish will be virtually invisible because no light will reflect from its surfaces.
B) the surfaces of the Pyrex will appear mirror-like-reflecting light perfectly as the result of total internal reflection.
C) the Pyrex dish will act as a lens and you will see highly distorted images of objects beyond the dish.
D) you will see a pattern of beautiful rainbow colors in the glass as dispersion separates white light.

Question 18

When white sunlight passes through a vase made of cut lead crystal, the light that emerges is often separated into brilliant colors. This coloration is due to the fact that

A) red light moves faster in lead crystal than violet light does.
B) lead crystal absorbs violet light more strongly than it absorbs red light.
C) red light experiences stronger Rayleigh scattering in lead crystal than violet light does.
D) lead crystal absorbs red light more strongly than it absorbs violet light.

Question 19

A glass window pane reflects about 4% of the light striking its front surface because

A) light slows down upon entering the glass and the resulting impedance mismatch causes some of that light to reflect.
B) glass is about 16% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.
C) glass is about 4% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.
D) glass is about 2% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.

Question 20

Sunsets are a deep red because

A) tiny particles in the air are more efficient at scattering short wavelength light than they are at scattering long wavelength light. Hence, long wavelength light ends up coming directly towards you.
B) most polluting gases and dust particles in the air are reddish in color and lend their color to that of the sky.
C) air molecules absorb red light more efficiently than they do blue light because of their electron orbitals.
D) air molecules absorb blue light more efficiently than they do red light because of their electron orbitals.

Question 21

Light passing from air into empty space will

A) speed up.
B) slow down.
C) not change speed.
D) Not enough information is given to determine.

Question 22

Light travels at about 300 million meters per second, and it takes light 100,000 years to go from one end of our galaxy to the other. How many miles across is our galaxy?

A) 100,000 m
B) 300,000,000 m
C) 9.3x10²⁰ m
D) 9.3x10²⁰ km

Question 23

Although sugar looks white, it is clear when placed in water (before dissolving) because

A) the optical environment outside the crystal is more dissimilar to that of the crystal itself and impedance mismatch has decreased..
B) the optical environment outside the crystal is closer to that of the crystal itself and impedance mismatch has decreased.
C) the optical environment outside the crystal is closer to that of the crystal itself and impedance mismatch has increased..
D) small sugar grains are metallic and act as mirrors, but mirrors don't work under water.

Question 24

You can get a sunburn on your face from sunlight reflecting off snow because

A) It is the ultraviolet light that burns you, and it reflects and scatters off the snow also.
B) The snow adds high energy light through resonance before it reflects.
C) The snow brightens the reflected a lot.
D) It is the cold weather - not the light -- that burns your face.

Question 25

A laser light beam can travel much farther than a flashlight without spreading out because laser light

A) has high energy .
B) is monochromatic.
C) is coherent.
D) is polarized.

Question 26

Suppose you are hired by a Hollywood firm to create a sunset on a planet just like the earth but where the sunlight was purely monochromatic and red. How should your set look?

Question 27

In what way is light from a sodium vapor lamp unlike sunlight?

A) It is created because something is hot (luminescing).
B) It is monochromatic.
C) It has too much blue.
D) It has too much red.

Question 28

There is a simple explanation for why bluer "cool white" fluorescent lamps are slightly more energy efficient than redder "warm white"
Lamps. It is because

A) a phosphor wastes more energy when converting an ultraviolet photon into red light than into blue light.
B) bluer lamps use higher currents and smaller voltages than redder lamps.
C) bluer lamps operate at higher temperatures than redder lamps and produce less invisible infrared light as a result.
D) bluer lamps use higher voltages and smaller currents than redder lamps.

Question 29

While low pressure sodium vapor lamps are the most energy efficient light sources commonly available, producing a pure orange-yellow light with a wavelength of 590 nanometers, high pressure sodium vapor lamps produce a richer spectrum of light that is more pleasing to the eye. One effect that contributes to this richer spectrum is

A) radiation trapping-in which the 590 nanometer light has trouble escaping from the lamp.
B) interference-in which light traveling to your eye via several paths within the lamp becomes brighter or darker, depending on how its electric fields interact with one another.
C) thermionic emission-in which electrons in the hot electrodes enter the gas of the discharge.
D) dispersion-in which the different colors of light travel at different speeds within the lamp.

Question 30

Suppose that you are stranded in a huge office building and are forced to build fluorescent lights without phosphors on the inside.
-If you run the lights with mercury vapor in them what kind of light will the bulbs apply to the office? Please explain.

Question 31

Suppose that you are stranded in a huge office building and are forced to build fluorescent lights without phosphors on the inside.
-If you want to replace the mercury vapor with some other vapor that will yield a lot more visible light , should the electron energy levels in the new material be closer together or farther apart? Please explain.

Question 32

Using three similarities and three differences please compare and contrast fluorescent light bulbs and incandescent light bulbs.

Question 33

What colors are the eye's color-sensing cells most sensitive to?

A) Red, yellow, and blue
B) Orange, green, and violet
C) Red, green, and violet
D) Red, green, and blue

Question 34

If you have a white light source and are able to subtract blue from it you will be left with

A) magenta.
B) cyan.
C) yellow.
D) red.

Question 35

The energy of a photon of red (wavelength 6.626x10^-7 m) light is

A) 3 J
B) 3x10^-19 J
C) 3x10^-20 Hz
D) 6.626x10^-19 J

Question 36

Light is emitted when electrons

A) disappear and then reappear.
B) jump down in energy level.
C) jump up in energy level.
D) turn into positrons

Question 37

In what way is light from a sodium vapor lamp like sunlight?

A) They both are luminescing.
B) They both are monochromatic.
C) They both are aerated by excited electrons.
D) They both include all colors.

Question 38

If you have a white light source and are able to subtract yellow from it you will be left with

A) magenta.
B) cyan.
C) yellow.
D) blue.

Question 39

Putting phosphors inside a sodium lamp is a poor idea because

A) It takes high energy light to make the phosphors glow and sodium does not produce enough of it.
B) They will be too bright for commercial use.
C) Their color cannot be controlled
D) The sodium vapor will react adversely with the phosphors.

Question 40

You work for a light company and you want to pleasantly surprise your boss. Would it work if you replaced the mercury vapor in fluorescent lights with something that makes more visible light so the lights would be brighter? Please explain.

Question 41

Using three similarities and three differences please compare and contrast fluorescent light bulbs and high pressure sodium lamps.

Question 42

"Laser" stands for

A) light amplification through stimulated emission of radiation.
B) light attenuation through stimulated emission of radiation.
C) light amplification through spontaneous emission of radiation
D) let's all study electromagnetic waves and refraction.

Question 43

Laser light is

A) polarized.
B) coherent.
C) incoherent.
D) incandescent.

Question 44

Three different lasers are emitting steady beams of light. Each beam consists of countless copies a single original photon of light. However, not all colors can be emitted by a laser. Which of the following choices is possible for these three lasers?

A) Yellow, green, and blue light
B) Green, blue, and white light
C) Blue, white, and yellow light
D) White, yellow, and green light

Question 45

Laser light exhibits much stronger interference effects than light from a flashlight. This is because

A) laser light has a much shorter wavelength than light from a flashlight.
B) laser light is both coherent and monochromatic.
C) laser light carries much more energy than light from a flashlight.
D) laser light travels as waves while light from a flashlight travels as particles.

Question 46

In a typical laser, the right color of light bounces back and forth between two mirrors and

A) is ignored by the laser medium.
B) is amplified by the mirrors.
C) is amplified by the excited atoms in the laser medium.
D) is de-amplified by the laser medium.

Question 47

When laser light reflects from a soap bubble, its photons can interfere with one another. In contrast, when sunlight reflects from a soap bubble, each photon can interfere only with itself. The reason for this difference is that

A) the photons in a laser beam are all part of a single wave, while those in sunlight are independent waves.
B) the photons in a laser beam have both electric and magnetic fields, while those in sunlight have only electric fields.
C) the photons in a laser beam have both electric and magnetic fields, while those in sunlight have only magnetic fields.
D) the photons in a laser beam are both vertically and horizontally polarized, while those in sunlight are only vertically polarized.

Question 48

A bright beam of light from a laser passes through a tiny pinhole on its way to a projection screen on the other side of the room. Since the beam was several millimeters in diameter, the pinhole blocks most of the beam's light. After passing through this pinhole, the remaining light

A) converges together rapidly to form an image of the laser on the projection screen.
B) forms an extremely narrow beam that illuminates only a tiny spot on the projection screen-a spot the same diameter as the pinhole.
C) changes frequency and color because it experiences destructive interference inside the pinhole.
D) spreads relatively rapidly so that it forms a rather large spot on the projection screen.

Question 49

The tubes in fluorescent lamps have a white powder on their inner surfaces. This powder

A) slows down the white light produced by the gas atoms inside the tube so that less of that white light reflects as it passes through the walls of the tube.
B) conducts electricity from one electrode to the other and emits visible light as current passes through it.
C) absorbs ultraviolet light and uses the energy from that light to produce visible light.
D) scatters the white light produced by the gas atoms inside the tube so that it is both vertically and horizontally polarized and doesn't cause glare.

Question 50

Some fiber optic communication systems use laser amplification to boost the intensity of light pulses passing through an optical fiber. A short segment of laser amplifier fiber is spliced into the main fiber so that the light pulses must pass through the laser amplifier fiber on their way to their destination. The light emerging from the laser amplifier fiber is much brighter than it was when it entered. One interesting aspect of the light emerging from the laser amplifier fiber is that it

A) has the same color as the light entering the amplifier fiber.
B) is slightly redder than the light entering the amplifier fiber-its wavelength is longer.
C) is slightly bluer than the light entering the amplifier fiber-its wavelength is shorter.
D) travels faster than the light entering the amplifier fiber.

Question 51

Explain why lasers can be used to perform surgery and cut through metal while incandescent light cannot.

Question 52

Please consider the red helium - neon laser. Now let's say your boss wants you to make a green laser, or else she'll make you take all your physics classes over again. So, you really want to build this laser right, and you decide that the crucial issue is replacing the neon with another gas. You can choose from a gas (gas A) whose light producing electron energy levels are all closer together than neon's, or from another (gas B) whose light producing energy levels are all father apart than those of neon.
-Which gas would you chose? Please explain.

Question 53

Please consider the red helium - neon laser. Now let's say your boss wants you to make a green laser, or else she'll make you take all your physics classes over again. So, you really want to build this laser right, and you decide that the crucial issue is replacing the neon with another gas. You can choose from a gas (gas A) whose light producing electron energy levels are all closer together than neon's, or from another (gas B) whose light producing energy levels are all father apart than those of neon.
-Now suppose your boss tricked you so that the mirrors in the laser did not reflect the green light - it just let the light through. Would this affect amplification and hence the brightness of the beam? Please explain.

Question 54

Suppose you are a school teacher and are doing a demonstration on how lasers work by sending wave pulses down ropes. You have many students and enough ropes for each pair of students to have a rope. Please describe how you would do the demonstration.

Question 55

A laser diode's wavelength and color depend primarily on

A) the band gap of its power supply
B) what it is hooked up to
C) the band gap of its anode
D) the density of its anode

Question 56

White LEDs are

A) LEDs that emit white light.
B) ultraviolet LEDs with phosphors inside.
C) infrared LEDs that heat up phosphors
D) yellow LEDs with a white coating on the inside.

Question 57

A CD reader uses laser light. What main difficulty would be encountered if white light were used?

Question 58

Suppose you view the light from an LED and from a laser diode through a prism. What would the main difference between the two types of light be?

Question 59

LED light is not damaging to your eye like a laser can be because

A) laser light is coherent while LED light is not.
B) laser light is monochromatic while LED light is not.
C) laser light is polarized.
D) laser light travels faster.

Question 60

A mercury street light gets brighter as it warms up because

A) the voltage across it is increasing.
B) the liquid mercury is flowing around more, making better connections.
C) more mercury is vaporizing.
D) it is getting darker outside and so it just looks brighter.

Question 61

What main difficulty would be encountered if an LED were used to read a DVD?

Question 62

A laser's output color depends primarily on

A) the power to it.
B) the energy gap between the upper and lower laser levels.
C) the energy gap between the lower laser level and ground state
D) how much lasing material is in the laser

Question 63

Suppose you are using a multi - floor building to demonstrate how laser light is emitted, and your students are electrons that can run between "energy levels" (floors). How many floors should your building have?