Problem Set 6
Due: see website for due date
Chapter 25: Reflection of Light: Mirrors
Questions: 12, 13, 14, 15
Problems: 6, 7, 15, 16, 20, 21, 30, 31
Q25.12: Which one of the following statements concerning spherical mirrors is correct?
(a) Only a convex mirror can produce an enlarged image. (b) Both concave and convex
mirrors can produce an enlarged image. (c) Only a concave mirror can produce an
enlarged image, provided the object distance is less than the radius of curvature. (d)
Only a concave mirror can produce an enlarged image, provided the object distance is
greater than the radius of curvature.
Q25.13: Suppose that you hold up a small convex mirror in front of your face. Which
answer describes the image of your face? (a) Virtual, inverted (b) Virtual, upright (c)
Virtual, enlarged (d) Real, inverted (e) Real, reduced in size.
Q25.14: An object is placed at a known distance in front of a mirror whose focal length is
also known. You apply the mirror equation and find that the image distance is a negative
number. This result tells you that _______. (a) the image is larger than the object (b) the
image is smaller than the object (c) the image is inverted relative to the object (d) the
image is real (e) the image is virtual.
Q25.15: An object is situated at a known distance in front of a convex mirror whose focal
length is also known. A friend of yours does a calculation that shows that the
magnification is −2. After some thought, you conclude correctly that _______. (a) your
friend’s answer is correct (b) the magnification should be +2 (c) the magnification should
be +1/2 (d) the magnification should be −1/2.
P25.6: The drawing shows a laser beam shining on a plane mirror
that is perpendicular to the floor. The beam’s angle of incidence is
33.08. The beam emerges from the laser at a point that is 1.10 m
from the mirror and 1.80 m above the floor. After reflection, how
far from the base of the mirror does the beam strike the floor?
Answer: 1.67 m
P25.7: Review Conceptual Example 1 as an aid in understanding this problem. The
drawings show two arrows, A and B, that are located in front of a plane mirror. A person
at point P is viewing the image of each arrow. Which images can be seen in their
entirety? Determine your answers by drawing a ray from the head and foot of each arrow
that reflects from the mirror according to the law of reflection and reaches point P. Only if
both rays reach point P after reflection can the image of that arrow be seen in its
entirety. Answer: Sees A in its entirety; does not see B in its entirety.
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P25.15: An object is placed 11 cm in front of a concave mirror whose focal length is 18
cm. The object is 3.0 cm tall. Using a ray diagram drawn to scale, measure (a) the
location and (b) the height of the image. The mirror must be drawn to scale.
Answer: 28 cm, 7.6 cm
P25.16: A 2.0-cm-high object is situated 15.0 cm in front of a concave mirror that has a
radius of curvature of 10.0 cm. Using a ray diagram drawn to scale, measure (a) the
location and (b) the height of the image. The mirror must be drawn to scale.
Answer: 7.5 cm, 1.0 cm
P25.20: The image behind a convex mirror (radius of curvature +68 cm) is located 22 cm
from the mirror. (a) Where is the object located and (b) what is the magnification of the
mirror? Determine whether the image is (c) upright or inverted and (d) larger or smaller
than the object. Answer: 62 cm, 0.35, upright, smaller
P25.21: A concave mirror (R = 56.0 cm) is used to project a transparent slide onto a
wall. The slide is located at a distance of 31.0 cm from the mirror, and a small flashlight
shines light through the slide and onto the mirror. The setup is similar to that in Figure
25.18a. (a) How far from the wall should the mirror be located? (b) The height of the
object on the slide is 0.95 cm. What is the height of the image? (c) How should the slide
be oriented, so that the picture on the wall looks normal?
Answer: 290 cm, 8.9 cm, upside down
P25.30: A dentist’s mirror is placed 2.0 cm from a tooth. The enlarged image is located
5.6 cm behind the mirror. (a) What kind of mirror (plane, concave, or convex) is being
used? (b) Determine the focal length of the mirror. (c) What is the magnification? (d)
How is the image oriented relative to the object? Answer: concave, 3.1 cm, 2.8, erect
P25.31: A tall tree is growing across a river from you. You would like to know the
distance between yourself and the tree, as well as its height, but are unable to make the
measurements directly. However, by using a mirror to form an image of the tree and
then measuring the image distance and the image height, you can calculate the distance
to the tree as well as its height. Suppose that this mirror produces an image of the sun,
and the image is located 0.9000 m from the mirror. The same mirror is then used to
produce an image of the tree. The image of the tree is 0.9100 m from the mirror. (a) How
far away is the tree? (b) The image height of the tree has a magnitude of 0.12 m. How
tall is the tree? Answer: 82 m, 11 m
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