Suppose you have two pinhole cameras. The first has a small round hole in the front. The second is identical except it has a square hole of the same area as the round hole in the first camera. Would the pictures taken by these two cameras, under the same conditions, be different in any obvious way? Explain.

You are looking at the image of a pencil in a mirror, as shown in FIGURE Q34.2.

1. What happens to the image if the top half of the mirror, down to the midpoint, is covered with a piece of cardboard? Explain.

2. What happens to the image if the bottom half of the mirror is covered with a piece of cardboard? Explain.

FIGURE Q34.2

One problem with using optical fibers for communication is that a light ray passing directly down the center of the fiber takes less time to travel from one end to the other than a ray taking a longer, zig-zag path. Thus light rays starting at the same time but traveling in slightly different directions reach the end of the fiber at different times. This problem can be solved by making the refractive index of the glass change gradually from a higher value in the center to a lower value near the edges of the fiber. Explain how this reduces the difference in travel times.

A light beam passing from medium 2 to medium 1 is refracted as shown in FIGURE Q34.4. Is $n_1$ larger than $n_2$, is $n_1$ smaller than $n_2$, or is there not enough information to tell? Explain.

FIGURE Q34.4

A fish in an aquarium with flat sides looks out at a hungry cat. To the fish, does the distance to the cat appear to be less than the actual distance, the same as the actual distance, or more than the actual distance? Explain.

Consider one point on an object near a lens.

1. What is the minimum number of rays needed to locate its image point? Explain.

2. How many rays from this point actually strike the lens and refract to the image point?

The object and lens in FIGURE Q34.7 are positioned to form a well-focused, inverted image on a viewing screen. Then a piece of cardboard is lowered just in front of the lens to cover the top half of the lens. Describe what you see on the screen when the cardboard is in place.

FIGURE Q34.7

A converging lens creates the image shown in FIGURE Q34.8. Is the object distance less than the focal length $f$, between $f$ and $2f$, or greater than $2f$? Explain.

FIGURE Q34.8

A concave mirror brings the sun’s rays to a focus in front of the mirror. Suppose the mirror is submerged in a swimming pool but still pointed up at the sun. Will the sun’s rays be focused nearer to, farther from, or at the same distance from the mirror? Explain.

You see an upright, magnified image of your face when you look into a magnifying cosmetic mirror. Where is the image? Is it in front of the mirror’s surface, on the mirror’s surface, or behind the mirror’s surface? Explain.

When you look at your reflection in the bowl of a spoon, it is upside down. Why?