Conceptual Questions

ssm Solution is in the Student Solutions Manual

| 1 | ssm A sign painted on a store window is reversed when viewed from inside the store. If a person inside the store views the reversed sign in a plane mirror, does the sign appear as it would when viewed from outside the store? (Try it by writing some letters on a transparent sheet of paper and then holding the back side of the paper up to a mirror.) Explain.

| 2 | If a clock is held in front of a mirror, its image is reversed left to right. From the point of view of a person looking into the mirror, does the image of the second hand rotate in the reverse (counter-clockwise) direction? Justify your answer.

| 3 | (a) Which kind of spherical mirror, concave or convex, can be used to start a fire with sunlight? (b) For the best results, how far from the mirror should the paper to be ignited be placed? Explain your answers.

| 4 | The photograph shows an experimental device at Sandia National Laboratories in New Mexico. This device is a mirror that focuses sunlight to heat sodium to a boil, which then heats helium gas in an engine. The engine does the work of driving a generator to produce electricity. The sodium unit and the engine are labeled in the photo. (a) What kind of mirror is being used, and (b) where is the sodium unit located relative to the mirror? Express your answer in terms of the focal length of the mirror. Give your reasoning.

| 5 | Refer to Figure 25-14 and the related discussion about spherical aberration. To bring the top ray closer to the focal point F after reflection, describe how you would change the shape of the mirror. Would you open it up to produce a more gently curving shape or bring the top and bottom edges closer to the principal axis? Account for your answer using the law of reflection.

| 6 | (a) Can the image formed by a concave mirror ever be projected directly onto a screen, without the help of other mirrors or lenses? If so, specify where the object should be placed relative to the mirror. (b) Repeat part (a) assuming that the mirror is convex.

| 7 | (a) When you look at the back side of a shiny teaspoon, held at arm’s length, you see yourself upright. Why? (b) When you look at the other side of the spoon, you see yourself upside down. Why?

| 8 | ssm If you stand between two parallel plane mirrors, you see an infinite number of images of yourself. This occurs because an image in one mirror is reflected in the other mirror to produce another image, which is then re-reflected, and so forth. The multiple images are equally spaced. Suppose that you are facing a convex mirror, with a plane mirror behind you. Describe what you would see and comment about the spacing between any multiple images. Explain your reasoning.

| 9 | Sometimes news personnel covering an event use a microphone arrangement that is designed to increase the ability of the mike to pick up weak sounds. The drawing shows that the arrangement consists of a hollowed-out shell behind the mike. The shell acts like a mirror for sound waves. Explain how this arrangement enables the mike to detect weak sounds.

| 10 | When you see the image of yourself formed by a mirror, it is because (1) light rays actually coming from a real image enter your eyes or (2) light rays appearing to come from a virtual image enter your eyes. If light rays from the image do not enter your eyes, you do not see yourself. Are there any places on the principal axis where you cannot see yourself when you are in front of a mirror that is (a) convex and (b) concave? If so, where are these places?

| 11 | Concept Simulation 25.3 at reviews the concepts that are important in this question. Plane mirrors and convex mirrors form virtual images. With a plane mirror, the image may be infinitely far behind the mirror, depending on where the object is located in front of the mirror. For an object in front of a single convex mirror, what is the greatest distance behind the mirror at which the image can be found? Justify your answer.

| 12 | Concept Simulation 25.3 at allows you to explore the concepts to which this question relates. Is it possible to use a convex mirror to produce an image that is larger than the object? Provide a reason for your answer.

| 13 | ssm Suppose you stand in front of a spherical mirror (concave or convex). Is it possible for your image to be (a) real and upright or (b) virtual and inverted? Justify your answers.

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