Deck 14: Optics and Electronics

Question 1

A lens which is thicker in the middle than at the edges is a

A) converging lens.
B) diverging lens.
C) achromatic lens.
D) antireflection lens.

Answer 1

converging lens.

Question 2

An object is very far from a converging lens with a short focal length. Where does the image form?

A) Far from the lens
B) Close to the lens
C) On the same side of the lens as the object
D) No image forms.

Answer 2

Close to the lens

Question 3

An object is very near a converging lens with a large focal length. Where does the image form?

A) At the focal point on the opposite side of the lens from the object.
B) On the opposite side of the lens as the object.
C) On the same side of the lens as the object.
D) No image forms.

Answer 3

On the same side of the lens as the object.

Question 4

A diaphragm is used to increase a lens' effective diameter. What effect does this have on the lens' f-number?

A) It increases.
B) It decreases.
C) It remains constant.
D) Not enough information is given to determine.

Question 5

Through a complex mechanism, both the effective diameter and the focal length of a lens are decreased. What happens to the lens' f-number?

A) It increases.
B) It decreases.
C) It remains constant.
D) Not enough information is given to determine.

Question 6

When using a magnifying glass to focus the Sun onto a piece of paper, the distance from the lens to the paper should be

A) less than the focal length of the lens.
B) equal to the focal length of the lens.
C) greater than the focal length of the lens.
D) Not enough information is given to determine.

Question 7

If you are viewing an object with a 7 Diopter lens and a 10 Diopter lens, which one has to be held closer to a piece of paper when focusing a distant object?

A) The 7 Diopter lens
B) The 10 Diopter lens
C) Both have the same focal length
D) Neither one will focus an image.

Question 8

You are observing a distant ship with a telescope but you cannot quite read the ship's name. To increase the magnification of the telescope, you replace the eyepiece with one having a

A) larger aperture than before.
B) smaller aperture than before.
C) shorter focal length than before.
D) longer focal length than before.

Question 9

To create a virtual magnified image of an object,

A) the object must be at the focal point of a concave lens.
B) the object must be just outside the focal point of a convex lens.
C) the object must be very far from a convex lens.
D) the object must be within the focal point of a convex lens.

Question 10

You are observing a distant building with a telescope and want to see small stones in the wall better. To increase the magnification of the telescope, you replace the objective with one having a

A) larger aperture than before.
B) smaller aperture than before.
C) shorter focal length than before.
D) longer focal length than before.

Question 11

Many sophisticated cameras have zoom lenses. When you select the telephoto setting, the objects in front of you appear much closer. In this setting,

A) the focal length of the lens is shorter than normal.
B) the aperture of the lens is larger than normal.
C) the focal length of the lens is longer than normal.
D) the aperture of the lens is smaller than normal.

Question 12

A good camera lens contains optical components in which two pieces of glass are glued directly together to form a single transparent object. These two-element optical components are important because they

A) bend light more efficiently than simple lenses.
B) reflect less light than simple lenses.
C) have larger depths of focus than simple lenses.
D) avoid the color focusing problems of simple lenses.

Question 13

Increasing the diameter of a camera lens, while keeping its focal length unchanged, does more than just brighten the image on the film so that you can use a shorter exposure. It also

A) decreases the depth of focus so that objects at different distances will no longer all be in focus at once.
B) increases the size of the image on the film so that you get a close up.
C) decreases the size of the image on the film so that you get a wide angle view.
D) increases the depth of focus so that objects at different distances will all be in focus at once.

Question 14

One advantage of using an enormous mirror to collect light in a telescope is that the real image is relatively bright. But there is also a benefit to letting the waves of starlight pass through the largest possible apertures. Sending a light wave through a small aperture truncates the wave severely and causes it to diffract. Because of this diffraction, light from a white star

A) forms a small rainbow of light in the real image.
B) forms a single spot of light in the real image, but not quite at the appropriate location.
C) forms a single spot of yellowish light in the real image.
D) spreads outward to form a fuzzy spot in the real image.

Question 15

Your small pocket camera has a telephoto setting in which the converging lens sticks far out in front of the camera body. The lens still projects a real image on film near the back of the camera body but now the lens is much farther from the film. When you shift the camera into this telephoto setting, the lens itself

A) effectively becomes more highly curved so that it bends light more strongly.
B) keeps its same curvature but its effective diameter becomes smaller.
C) effectively becomes less highly curved so that it bends light less strongly.
D) keeps its same curvature but its effective diameter becomes larger.

Question 16

A reflecting telescope has the advantage that its main optic has only one element (a curved mirror) and that this element does not have to be made of transparent material. In contrast, the simplest high-quality refracting telescope needs two elements in its main optic (a converging lens) and both elements must be perfectly transparent. It needs these two transparent elements in its lens because a single element lens

A) can only form a virtual image and not a real image.
B) causes light to spread apart rather than come together.
C) will produce an inverted real image while a two element lens will produce an upright real image.
D) cannot bring all the colors to a focus at the same distance.

Question 17

Explain why taking nice sharp pictures with large depths of field in very dimly lit environments can be very challenging to photographers.

Question 18

Dispersion affects photographs in that an object may seem blurred and separated into different colors when reflecting or emitting white light (a full spectrum). What changes would have to happen to the spectrum of light reaching you from the object for
-dispersion to have a lesser effect on the pictures?

Question 19

Dispersion affects photographs in that an object may seem blurred and separated into different colors when reflecting or emitting white light (a full spectrum). What changes would have to happen to the spectrum of light reaching you from the object for
-How about for dispersion to have no effect?

Question 20

Suppose you have a camera and you notice that the pictures you are taking are out of focus. Please describe three changes you could make to the lens only that would help you get sharper pictures. Please assume that the camera is one that can not be focused but you can just change any aspect of the lens.

Question 21

An object is 10 m from a convex lens and an image forms on the other side of the lens, 20 m away. The focal length of the lens is

A) -20 m
B) 20 m
C) - 20/3 m
D) 20/3 m

Question 22

A nearsighted person's eyes

A) refract light too little and focus images of distant objects in front of the retina.
B) refract light too much and focus images of distant objects behind the retina.
C) refract light too much and focus images of distant objects in front of the retina.
D) have pupils that are too small.

Question 23

A farsighted person's eyes

A) refract light too little and focus images of distant objects in front of the retina.
B) refract light too little and would focus images of distant objects behind the retina.
C) refract light too much and focus images of distant objects in front of the retina.
D) have pupils that are too small.

Question 24

If you lose your eyeglasses, it is suggested that you make a very small hole with your fist and look through it. Explain how this can help you see more clearly.

Question 25

A lens which is thinner in the middle than at the edges is a

A) converging lens.
B) diverging lens.
C) achromatic lens.
D) antireflection lens.

Question 26

The speed of light in glass is

A) smaller than that in air.
B) larger than that in air.
C) unchanged from that in air.
D) undefined.

Question 27

To create a real inverted image of an object,

A) the object must be at the focal point of a concave lens.
B) the object must be outside the focal point of a convex lens.
C) the object must be very close to a convex lens.
D) the object must be within the focal point of a convex lens.

Question 28

Explain why taking nice sharp pictures with large depths of field in very brightly lit environments is fairly easy for photographers.

Question 29

Suppose you could take a converging lens underwater and try to focus the sun on the bottom of a swimming pool. You will find that

A) the lens has to be closer to the image than in air.
B) the lens has to be the same distance to the image as in air.
C) the lens has to be farther from the image than in air.
D) in general an image can't be formed at all.

Question 30

Suppose you could take a telescope mirror underwater and try to focus the sun with it.

A) the mirror has to be closer to the image than in air.
B) the mirror behaves the same as it did in air.
C) the mirror has to be farther from the image than in air.
D) in general an image can't be formed at all.

Question 31

Suppose you are stranded on a desert island with the publisher of your physics text. You need to start a fire and to do this you decide to focus the sun wit eyeglasses. Your book publisher knows about physics and so they will use the glasses of someone who is

A) astigmatic.
B) farsighted.
C) nearsighted
D) myopic

Question 32

In a CD player, light from a laser diode enters a plastic disc and reflects from a layer of shiny aluminum. Before it enters the plastic, the laser light has a wavelength of 780 nanometers and a frequency of 385,000,000,000,000 Hz. Once this light is inside the plastic, its wavelength

A) stays the same but its frequency becomes higher.
B) becomes shorter but its frequency stays the same.
C) becomes longer but its frequency stays the same.
D) stays the same but its frequency becomes lower.

Question 33

Which of the following does not limit how much information can be stored on a CD or DVD?

A) Wavelength of the light used to read it
B) Diffraction limits on the pit size
C) Diffraction limits on the track spacing
D) Machine limits on how small pits can be made

Question 34

What is the main reason a DVD can hold more information than a CD, aside from the number of layers of data storage medium?

A) DVD's use polarized light.
B) CD's are diffraction limited
C) DVD's use shorter-wavelength light than CDs
D) CD light is circularly polarized

Question 35

Optical fibers work using the principle of

A) dispersion shifting.
B) total internal reflection.
C) erbium-doped fiber amplification.
D) diffraction limitation.

Question 36

Optical communications transmitters most often use light in what region of the spectrum?

A) Ultraviolet
B) Visible
C) Infrared
D) Both visible and infrared

Question 37

The standard wavelength of light that is used in CD readers is

A) 780 nm
B) 880 nm
C) 580 nm
D) 700 nm

Question 38

A glass fiber can act as a pipe for light-light that enters the fiber at its end follows the fiber almost indefinitely without escaping through the fiber's surface. The light follows the fiber because

A) electric charges in the glass attract the light and prevent it from accelerating outward, away from the center of the fiber.
B) the fiber contains many tiny diverging lenses that focus the light back into the fiber over and over again.
C) whenever it tries to leave the glass at a shallow angle, it's perfectly reflected.
D) the fiber contains many tiny converging lenses that focus the light back into the fiber over and over again.

Question 39

At present, a compact disc can only hold about 1 hour of music. This limit is due in large part to the fact that

A) a compact disc cannot turn faster than about 5 turns per second without experiencing a net torque of zero.
B) light cannot be focused to a spot that is significantly smaller than its wavelength.
C) the ridges in the aluminum layer of the compact disc cannot experience destructive interference unless they have a wavelength that is almost equal to the distance between them.
D) a compact disc cannot turn slower than about 5 turns per second without experiencing a net torque of zero.

Question 40

You are in Corpus Christi on vacation and are diving. Underwater, you notice that if you do not look at your watch directly there is an angle where the surface looks just like a mirror. Please explain.

Question 41

You are working for a company that designs CDs. A co-worker and you are having an argument about light. You claim that you measure a particular wavelength of light in a vacuum to have a certain value and when your co-worker goes to calculate the wavelength of light in plastic they get a different value. Is your co-worker's value higher or lower than yours? Please explain the discrepancy.

Question 42

In a CD player, light from a laser diode enters a plastic disc and reflects from a layer of shiny aluminum. In the plastic, the laser light has a wavelength of

A) greater than 780 nanometers
B) 780 nanometers
C) less than 780 meters
D) 3x10⁸ m

Question 43

In a CD player, light from a laser diode enters a plastic disc and reflects from a layer of shiny aluminum. Before it enters the plastic, the laser light has a frequency of

A) 385,000,000,000,000,000 Hz
B) 385,000,000,000 Hz
C) 385,000,000,000,000 Hz.
D) 385,000 Hz

Question 44

A CD or DVD player uses a

A) laser diode
B) Zener diode.
C) conventional diode.
D) reverse biased diode.

Question 45

Laser light goes from air, through a focusing lens and then back into air. In doing so it

A) speeds up twice.
B) slows down and then speeds up
C) slows down once.
D) slows down twice.

Question 46

We do not notice total internal reflection for regular glass store windows because

A) light travels slower in glass than in air.
B) glass does not have a suitable chemical makeup.
C) light travels too fast in glass.
D) glass is transparent and has no metal in it.

Question 47

In order for us to notice total internal reflection in everyday glass store windows,

A) glass would have to have some metal in it.
B) light would have to travel slower in air than in glass.
C) light would have to travel slower in glass than in air
D) all vibration from the street would have to cease.

Question 48

The data used by an audio player contains

A) NAND gates and inverters.
B) n-channel MOSFETs.
C) information on pressure measurements.
D) varying voltages.

Question 49

MOSFET stands for

A) multi-open-source fixed emission transistor.
B) mixed omni-source field emitting transistor.
C) metal-oxide semiconductor field-effect transistor.
D) metal-oxide semiconductor fixed emission transistor.

Question 50

How does an n-channel MOSFET work?

A) A p-type channel is sandwiched between an n-type source and an n-type drain. By putting a negative charge on a metal-like gate, current is allowed to flow.
B) A p-type channel is sandwiched between an n-type source and an n-type drain. By putting a positive charge on a metal-like gate, current is allowed to flow.
C) An n-type channel is sandwiched between a p-type source and a p-type drain. By putting a negative charge on a metal-like gate, current is allowed to flow.
D) An n-type channel is sandwiched between a p-type source and a p-type drain. By putting a positive charge on a metal-like gate, current is allowed to flow.

Question 51

Putting more positive charge on the gate in an n-channel MOSFET causes

A) it to turn off.
B) the amount of current that can be handled to increase.
C) the amount of current that can be handled to decrease.
D) nothing. n-channel MOSFETs are controlled by putting negative charge on the gate.

Question 52

When an n-channel MOSFET is turned on,

A) the channel, which is p-type, acts like an n-type semiconductor.
B) the channel, which is n-type, acts like a p-type semiconductor.
C) the drain changes from p-type to n-type.
D) the source changes from n-type to p-type.

Question 53

The binary number 00110101 stands for what decimal number?

A) 29
B) 51
C) 53
D) 101

Question 54

In binary, the decimal number 87 is represented by:

A) 01011011
B) 00110101
C) 10011010
D) 01010111

Question 55

An example of volatile memory is

A) flash.
B) RAM.
C) hard disk.
D) optical disk.

Question 56

In dynamic memory,

A) the information is retained if the power is turned off.
B) information may only be written a limited number of times due to physical limitations.
C) the information that is stored is effectively permanent.
D) the information that is stored must be regularly rewritten or it will be lost.

Question 57

In flash memory,

A) the information is not retained if the power is turned off.
B) information may only be written a limited number of times due to physical limitations.
C) the information that is stored is volatile.
D) the information that is stored must be regularly rewritten or it will be lost.

Question 58

In flash memory,

A) reading information is fast but writing it is slow.
B) reading information is slow but writing it is fast.
C) both reading and writing information are slow.
D) both reading and writing information are fast.

Question 59

A NAND gate receives a 0 and a 1 as input. The output will be

A) 0
B) 1
C) 00
D) 11

Question 60

An inverter receives a 1 as input. The output will be

A) 0
B) 1
C) 00
D) 11

Question 61

In principal, an entire computer could be built out of

A) NAND gates and NOR gates.
B) AND gates and OR gates.
C) NAND gates and inverters.
D) NAND gates alone.

Question 62

In an amplifier,

A) a small fluctuating input current produces a large fluctuating output current.
B) a large fluctuating input current produces a small fluctuating output current.
C) a small fluctuating input current produces a large fixed output current.
D) a small fixed input current produces a large fluctuating output current.

Question 63

What is the effect of feedback in an amplifier?

A) The input signal is fed back onto itself to become larger.
B) It keeps the amplifier at a stable equilibrium which is sensitive to tiny changes in the gate charge.
C) The feedback is very fast, allowing the amplifier to react quickly to changes in the input voltage.
D) The feedback serves to keep the output current at a stable level.

Question 64

To transfer information between two circuits at different voltages, you can use

A) a NAND gate.
B) an inverter.
C) a capacitor.
D) an n-channel MOSFET.

Question 65

What happens when positive charge accumulates on one plate of a capacitor?

A) A larger amount of negative charge is pulled to the other plate, and the capacitor as a whole becomes more negative.
B) The other plate also becomes positive.
C) Some negative charge is pulled to the other plate, but the capacitor as a whole becomes more positive.
D) Negative charge is pulled to the other plate, but the capacitor as a whole remains neutral.

Question 66

How is a CMOS NAND gate built?

A) It has two n-channel MOSFETs and two p-channel MOSFETs, all in series.
B) It has two n-channel MOSFETs and two p-channel MOSFETs, all in parallel.
C) It has two n-channel MOSFETs in parallel and two p-channel MOSFETs in series.
D) It has two n-channel MOSFETs in series and two p-channel MOSFETs in parallel.