Physics 21
Practice Midterm #3 Problems
Name _____________________
Chapter 23
c 1. You stand two feet away from a plane mirror. What is the distance between you and your image?
a. 2.0 ft
b. 3.0 ft
c. 4.0 ft
d. 5.0 ft
c 2. Which of the following best describes the image from a plane mirror?
a. virtual and magnification greater than one
b. real and magnification less than one
c. virtual and magnification equal to one
d. real and magnification equal to one
c 3. How large should a wall-mounted mirror be to view the upper half of ones height, h?
a. h
b. h/2
c. h/4
d. The answer is not given.
b 4. Which of the following best describes the image for a thin convex lens that forms whenever the object is at a distance
less than one focal length from the lens?
a. inverted, enlarged and real
b. upright, enlarged and virtual
c. upright, diminished and virtual
d. inverted, diminished and real
c 5. Which of the following best describes the image for a thin concave lens that forms whenever the magnitude of the
object distance is less than that of the lens' focal length?
a. inverted, enlarged and real
b. upright, enlarged and virtual
c. upright, diminished and virtual
d. inverted, diminished and real
d 6. A convex mirror with focal length of 20 cm forms an image 12 cm behind the surface. Where is the object located as
measured from the surface?
SHOW WORK
a. 7.5 cm
b. 15 cm
c. 22 cm
d. 30 cm
a 7.
An object is held at a distance of 12 cm from a convex mirror creating an image that is 1/3 the object size. What is
the focal length of the mirror?
SHOW WORK
a. 6.0 cm
b. 3.0 cm
c. 9.0 cm
d. 18 cm
a 8. An object is placed at a distance of 50 cm from a thin lens along the axis. If a real image forms at a distance of 40 cm
from the lens, on the opposite side from the object, what is the focal length of the lens?
SHOW WORK
a. 22 cm
b. 45 cm
c. 90 cm
d. 200 cm
b 9. Ellen places an object 40.0 cm from a concave lens. If a virtual image appears 10.0 cm from the lens on the same side
as the object, what is the focal length of the lens?
SHOW WORK
a. 50.0 cm
b. 13.3 cm
c. 10.0 cm
d. 8.00 cm
Chapter 24
c 10. Interference effects observed in the early 1800’s were instrumental in supporting a concept of the existence of
which property of light?
a. polarization
b. particle nature
c. wave nature
d. electromagnetic character
b 11. Two beams of coherent light are shining on the same piece of white paper. With respect to the crests and troughs
of such waves, darkness will occur on the paper where:
a. the crest from one wave overlaps with the crest from the other.
b. the crest from one wave overlaps with the trough from the other.
c. the troughs from both waves overlap.
d. darkness cannot occur as the two waves are coherent.
a 12. In a Young’s experiment, the paths from the slits to a point on the screen differ in length causing destructive
interference at the point. Which of the following path difference would cause this destructive interference?
a. 5λ/2
b. 3λ/4
c. 4λ
d. none of the above
c 13. In a Young’s experiment, the paths from the slits to a point on the screen differ in length causing constructive
interference at the point. Which of the following path difference would cause this constructive interference?
a. 5λ/2
b. 3λ/4
c. 4λ
d. none of the above
b 14. Two narrow slits are 0.025 mm apart. When a laser shines on them, bright fringes form on a screen that is a meter
away. These fringes are 3.0 cm apart. What is the separation between the second order bright fringe and the central
fringe?
SHOW WORK
a. 8.6 cm
b. 6.0 cm
c. 5.3 cm
d. 2.6 cm
d 15. In a Young’s double-slit interference apparatus, by what factor is the distance between adjacent light and dark
fringes changed when the wavelength of the source is doubled?
SHOW WORK
a. 1/4
b. 1/2
c. 1
d. 2
b 16. A Young’s double-slit apparatus is set up where a screen is positioned 0.80 m from the double slits. If the distance
between alternating bright fringes is 0.95 cm and the light source has a wavelength of 580 nm, what is the separation
of the double slits? (1 nm = 109 m)
SHOW WORK
a. 2.8  105 m
b. 4.9  105 m
c. 5.6  105 m
d. 6.0  105 m
c 17. If the 2nd order fringe in Young’s double-slit experiment occurs at an angle of 45.0º, what is the relationship
between the wavelength  and the distance between slits, d?
SHOW WORK
a. d = 1.41
b. d = 2.00
c. d = 2.83
d. d = 4.00
b18. A Young’s interference experiment is conducted with blue-green argon laser light ( = 515 nm). The separation
between the slits is 0.50 mm and the interference pattern appears on a screen 3.3 m away. What is the spacing
between the bright fringes? (1 nm = 109 m)
SHOW WORK
a. 1.7 mm
b. 3.4 mm
c. 5.1 mm
d. 6.8 mm
Chapter 25
c 19.
A diverging lens will be prescribed by the eye doctor to correct which of the following?
a. farsightedness
b. glaucoma
c. nearsightedness
d. astigmatism
c 20.
The pupil of the eye reduces in size under which condition?
a. eye is focused on a distant object
b. eye is focused on a nearby object
c. object viewed is well illuminated
d. object viewed is dimly illuminated
a 21.
A lens with a focal length of 20 cm has what power?
a. 5.0 diopters
b. 6.7 diopters
c. 8.0 diopters
d. 9.6 diopters
c 22. What is the f-number of a camera lens that has an aperture-opening diameter of 0.30 cm and a focal length of 3.0
cm?
a. 0.10
b. 0.80
c. 10
d. 15
b 23.
Tripling the aperture diameter of a camera lens will change the f-number by what factor?
a. 1/9
b. 1/3
c. 3
d. 9
c 24. Tripling the focal length in a telephoto lens, while keeping the aperture size constant, will change the f-number by
what factor?
a. 1/9
b. 1/3
c. 3
d. 9
c 25. You are designing eyeglasses for someone whose near point is 60 cm. What focal length lens should you
prescribe so that an object can be clearly seen when placed at 25 cm in front of the eye?
a. 15 cm
b. 18 cm
c. 43 cm
d. 60 cm
a 26. A given individual is unable to see objects clearly when they are beyond 100 cm. What focal length lens should
be used to correct this problem?
a. 100 cm
b. 33.3 cm
c. 20 cm
d. 75 cm