Conceptual Physics Fundamentals

Paul G. Hewitt

Chapter 14

Properties of Light - all with Video Answers

Educators

Chapter Questions

Problem 1

Her eye at point $P$ looks into the mirror. Which of the numbered cards can she see reflected in the mirror?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 2

Cowboy Joe wishes to shoot his assailant by ricocheting a bullet off a mirrored metal plate. To do so, should he simply aim at the mirrored image of his assailant? Explain.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 3

Trucks often have signs on their backsides that say, "If you can't see my mirrors, I can't see you." Explain the physics here.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 4

Why is the lettering on the front of some vehicles, for example ambulances, "backward"?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 5

When you look at yourself in the mirror and wave your right hand, your beautiful image waves its left hand. Then why don't the feet of your image wiggle when you shake your head?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 6

Car mirrors are uncoated on the front surface and silvered on the back surface. When the mirror is properly adjusted, light from behind reflects from the silvered surface into the driver's eyes. Good. But this is not so good at nighttime with the glare of headlights behind. This problem is solved by the wedge shape of the mirror (see sketch). When the mirror is tilted slightly upward to the "nighttime" position, glare is directed upward toward the ceiling, away from the driver's eyes. Explain how the driver can still see cars behind in the mirror.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 7

To reduce the glare of the surroundings, the windows of some department stores slant inward at the bottom, rather than being vertical. How does this reduce glare?

Keshav Singh

Numerade Educator

Problem 8

A person in a dark room looking through a window can clearly see a person outside in the daylight, whereas the person outside cannot see the person inside. Explain.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 9

Which kind of road surface is easier to see when driving at night, an uneven pebbled surface or a mirror-smooth surface? Explain.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 10

Why is it difficult to see the roadway in front of you when driving on a rainy night?

Keshav Singh

Numerade Educator

Problem 11

We see the bird and its reflection. Why do we not see the bird's feet in the reflection?

Eduard Sanchez

Numerade Educator

Problem 12

What must be the minimum length of a plane mirror in order for you to see a full view of yourself?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 13

What effect does your distance from the plane mirror have on your answer to the preceding question? (Try it and see!) Hold a pocket mirror almost at arm's length from your face and note the amount of your face you can see. To see more of your face, should you hold the mirror closer or farther, or would you have to have a larger mirror? (Try it and see!)

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 15

From a steamy mirror, wipe away just enough steam to allow you to see your full face. How tall will the wiped area be compared with the vertical dimension of your face?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 16

The diagram shows a person and her twin at equal distances on opposite sides of a thin wall. Suppose that a window were to be cut in the wall so each twin can see a complete view of the other. Show the size and location of the smallest window that could be cut in the wall to do the job. (Hint: Draw rays from the top of each twin's head to the other twin's eyes. Do the same from the feet of each to the eyes of the other.)

Keshav Singh

Numerade Educator

Problem 17

Why does reflected light from the Sun or Moon appear as a column in the body of water as shown? How would it appear if the water's surface were perfectly smooth?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 18

What is wrong with the cartoon of the man looking at himself in the mirror? (Have a friend face a mirror as shown, and you'll see.)

Keshav Singh

Numerade Educator

Problem 19

A pair of toy cart wheels is rolled obliquely from a smooth surface onto two plots of grass, a rectangular plot and a triangular plot, as shown. The ground is on a slight incline, so that, after slowing down in the grass, the wheels will speed up again when emerging onto the smooth surface. Finish the sketches by showing some positions of the wheels inside each plot and on the other side of each plot, thereby indicating their direction of travel.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 20

A pulse of red light and a pulse of blue light enter a glass block normal to its surface at the same time. Strictly speaking, after passing through the block, which pulse exits first?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 21

During a lunar eclipse, the Moon is not completely dark, but it is often a deep red in color. Explain this in terms of the refraction of all the sunsets and sunrises around the world.

Keshav Singh

Numerade Educator

Problem 22

If you place a glass test tube in water, you will be able to see the tube. If you place it in clear soybean oil, you may not be able to see it. What does this tell you about the speed of light in the oil and in the glass?

Hubert Agamasu

Numerade Educator

Problem 23

If, while standing on the bank of a stream, you wished to spear a fish swimming in the water out in front of you, would you aim above, below, or directly at the observed fish to make a direct hit? If you decided instead to zap the fish with a laser, would you aim above, below, or directly at the observed fish? Defend your answers.

Keshav Singh

Numerade Educator

Problem 24

If the fish in the previous exercise were small and blue, and your laser light were red, what corrections should you make? Explain.

Keshav Singh

Numerade Educator

Problem 25

When a fish looks upward at an angle of $45^{\circ},$ does it see the sky or only the reflection of the bottom? Defend your answer.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 26

If you were to send a beam of laser light to a space station above the atmosphere and just above the horizon, would you aim the laser above, below, or directly at the visible space station? Defend your answer.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 27

Rays of light in water that shine up to the water-air boundary at angles of more than $48^{\circ}$ to the normal are totally reflected. No rays beyond $48^{\circ}$ refract outside. How about the other way around? Is there an angle at which light rays in air meeting the air-water boundary will reflect totally? Or will some light be refracted at all angles?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 28

When your eye is submerged in water, is the bending of light rays from water to your eyes greater than, less than, or the same as it is in air?

Keshav Singh

Numerade Educator

Problem 29

When you stand with your back to the Sun, you see a rainbow as a circular arc. Could you move off to one side and then see the rainbow as the segment of an ellipse rather than the segment of a circle (such as Figure 20 suggests)? Defend your answer.

Prashant Bana

Numerade Educator

Problem 30

Two observers standing apart from one another do not see the "same" rainbow. Explain.

Keshav Singh

Numerade Educator

Problem 31

A rainbow viewed from an airplane may form a complete circle. Where will the shadow of the airplane appear? Explain.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 32

How is a rainbow similar to the halo sometimes seen around the Moon on a frosty night? How are rainbows and halos different?

Ajay Singhal

Numerade Educator

Problem 33

What is responsible for the rainbow-colored fringe commonly seen at the edges of a spot of white light from the beam of a lantern or slide projector?

Prashant Bana

Numerade Educator

Problem 34

Transparent plastic swimming-pool covers called solar heat sheets have thousands of small lenses made up of air-filled bubbles. The lenses in these sheets are advertised to focus heat from the Sun into the water and raise its temperature. Do you think the lenses of such sheets direct more solar energy into the water? Defend your answer.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 35

Would the average intensity of sunlight measured by a light meter at the bottom of the pool in Figure 34 be different if the water were still?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 36

What accounts for the large shadows cast by the ends of the thin legs of the water strider? What accounts for the ring of bright light around the shadows on the botrom?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 37

Why will goggles allow a swimmer underwater to focus more clearly on what he is looking at?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 38

Cover the top half of a camera lens. What effect does this have on the pictures taken?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 39

Would refracting telescopes and microscopes magnify if light had the same speed in glass as it does in air? Explain.

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 40

Consider a simple magnifying glass underwater. Will it magnify more or less? Explain why.

Ajay Singhal

Numerade Educator

Problem 41

Can you take a photograph of your image in a plane mirror and focus the camera both on your image and on the mirror frame? Explain.

Hubert Agamasu

Numerade Educator

Problem 42

For correct viewing, why are slides put into a slide projector upside down?

Keshav Singh

Numerade Educator

Problem 43

Maps of the Moon are upside down. Why?

Sri Datta Vikas Buchemmavari

Sri Datta Vikas Buchemmavari

Numerade Educator

Problem 44

What does polarization tell you about the nature of light waves?

Caitlin Walker

Numerade Educator

Problem 45

The digital displays of watches and other devices are normally polarized. What problem occurs with these displays when one is wearing polarized sunglasses?

Prabhu Ramji

Numerade Educator

Problem 46

Why will an ideal Polaroid filter transmit $50 \%$ of incident nonpolarized light?

Andrew Eddins

Emory University

Problem 47

Why may an ideal Polaroid filter transmit anything from zero to $100 \%$ of incident polarized light?

Prabhu Ramji

Numerade Educator

Problem 48

What percentage of light is transmitted by two ideal Polaroid filters, one on top of the other with their polarization axes aligned? With their polarization axes at right angles to each other?

Ben Nicholson

Numerade Educator

Problem 49

How can a single Polaroid filter be used to show that the sky is partially polarized? (Interestingly enough, unlike humans, bees and many insects can discern polarized light, and they use this ability for navigation.)

Prabhu Ramji

Numerade Educator

Problem 50

Light will not pass through a pair of Polaroid filters when they are aligned perpendicularly. But, if a third Polaroid filter is sandwiched between the other two with its alignment halfway between the alignments of the others (that is, with its axis making a $45^{\circ}$ angle with each of the other two alignment axes), some light does get through. Why?

Ben Nicholson

Numerade Educator