Physics 103
Spring 2008
Take-home Quiz 3 Chapter 23
Please circle the correct answer
1) A plane mirror forms an image that is
A) real and upright.
B) virtual and upright.
C) real and upside down.
D) virtual and upside down.
2) Plane mirrors produce images which
A) are always smaller than the actual object.
B) are always larger than the actual object.
C) are always the same size as the actual object.
D) could be smaller, larger, or the same size as the actual object, depending on the placement of
the object.
3) Is it possible to see a virtual image?
A) No, since the rays that seem to emanate from a virtual image do not in fact emanate from the
image.
B) No, since virtual images do not really exist.
C) Yes, the rays that appear to emanate from a virtual image can be focused on the retina just like
those from an illuminated object.
D) Yes, since almost everything we see is virtual because most things do not themselves give off
light, but only reflect light coming from some other source.
E) Yes, but only indirectly in the sense that if the virtual image is formed on a sheet of
photographic film, one could later look at the picture formed.
4) A light ray, traveling parallel to a concave mirror's axis, strikes the mirror's surface near its
midpoint. After reflection, this ray
A) again travels parallel to the mirror's axis.
B) travels at right angles to the mirror's axis.
C) passes through the mirror's center of curvature.
D) passes through the mirror's focal point.
5) An object is positioned between a concave mirror's center of curvature and its focal point.
The image produced by the mirror is located
A) out past the center of curvature.
B) at the center of curvature.
C) between the center of curvature and the focal point.
D) at the focal point.
6) A negative magnification for a mirror means
A) the image is inverted, and the mirror is concave.
B) the image is inverted, and the mirror is convex.
C) the image is inverted, and the mirror may be concave or convex.
D) the image is upright, and the mirror is convex.
E) the image is upright, and the mirror may be concave or convex.
7) The index of refraction of diamond is 2.42. This means that a given frequency of light travels
A) 2.42 times faster in air than it does in diamond.
B) 2.42 times faster in diamond than it does in air.
C) 2.42 times faster in vacuum than it does in diamond.
D) 2.42 times faster in diamond than it does in vacuum.
8) A ray of light, which is traveling in air, is incident on a glass plate at a 45° angle. The angle
of refraction in the glass
A) is less than 45°.
B) is greater than 45°.
C) is equal to 45°.
D) could be any of the above; it all depends on the index of refraction of glass.
9) The critical angle for a beam of light passing from water into air is 48.8°. This means that all
light rays with an angle of incidence greater than this angle will be
A) absorbed.
B) totally reflected.
C) partially reflected and partially transmitted.
D) totally transmitted.
10) Lenses that are thicker at the center
A) spread out light rays.
B) bend light rays to a point beyond the lens.
C) have no effect on light rays.
D) reflect light rays back.
12) The images formed by concave lenses
A) are always real.
B) are always virtual.
C) could be real or virtual; it depends on whether the object distance is smaller or greater than the
focal length.
D) could be real or virtual, but always real when the object is placed at the focal point.
13) How fast do you approach your image when you approach a vertical plane mirror at a speed
of 2 m/s?
A) 1 m/s
B) 2 m/s
C) 4 m/s
D) none of the given answers
Please calculate the following problems, showing your work, and circle the correct
answer. To receive full credit, you must show your work.
14) A concave mirror with a radius of 20 cm creates a real image 30 cm from the mirror. What
is the object distance?
A) 20 cm
B) 15 cm
C) 7.5 cm
D) 5.0 cm
15) When a person stands 40 cm in front of a cosmetic mirror (concave mirror), the erect image
is twice the size of the object. What is the focal length of the mirror?
A) 27 cm
B) 40 cm
C) 80 cm
D) 160 cm
16) If a material has an index of refraction of 1.50, what is the speed of light through it?
A) 2.00 × 108 m/s
B) 3.00 × 108 m/s
C) 4.50 × 108 m/s
D) 6.00 × 108 m/s
17) An oil layer that is 5.0 cm thick is spread smoothly and evenly over the surface of water on a
windless day. What is the angle of refraction in the water for a ray of light that has an angle of
incidence of 45° as it enters the oil from the air above? (The index of refraction for oil is 1.15,
and for water it is 1.33.)
A) 27°
B) 32°
C) 36°
D) 39°
18) What is the critical angle for light traveling from crown glass (n = 1.52) into water (n =
1.33)?
A) 42°
B) 48°
C) 57°
D) 61°
19) An object is 12 cm in front of a converging lens with focal length 4 cm. Where is the image?
A) 8.0 cm behind the lens
B) 6.0 cm in front of the lens
C) 6.0 cm behind the lens
D) 4.0 cm in front of the lens
20) An object is 15.2 mm from a converging lens. The image is 4.0 mm tall, and 9.0 cm from
the lens. How tall is the object?
A) 6.8 mm
B) 5.4 mm
C) 1.7 mm
D) 0.68 mm