Chapter 25 Interference and Diffraction
1. A general condition that two waves undergo constructive interference is that:
A. their phase difference is zero.
B. their phase difference is π/2 rad.
C. their phase difference is ±π/2 rad.
D. their phase difference is an even integral multiple of π rad.
E. their phase difference is an odd integral multiple of π rad.
2. A general condition that two waves undergo destructive interference is:
A. their phase difference is zero.
B. their phase difference is π/2 rad.
C. their phase difference is ±π/2 rad.
D. their phase difference is an even integral multiple of π rad.
E. their phase difference is an odd integral multiple of π rad.
3. Two coherent sources emit waves of 2.0-m wavelength in phase. If the path length to an observer differs by
________, then _________ interference occurs.
A. 1.0 m, constructive
B. 2.0 m, destructive
C. 3.5 m, constructive
D. 7.0 m, destructive
E. 8.0 m, destructive
4. Two coherent waves, each with amplitude A, reach the same point in phase. The amplitude of the superposed
wave is:
A. 0.
B. A.
C. 2 A.
D. 3 A.
E. 4 A.
8. If two coherent waves, one with intensity 8.0 units and the other with intensity 4.0 units, undergo destructive
interference, what is the resulting intensity?
A. 4.0 units
B. 6.0 units
C. -4.0 units
D. 1.9 units
E. 0.7 units
11. A thin film of soapy water, n = 1.37, is held vertical. Light of wavelength 600 nm is reflected from the film
and horizontal dark lines appear. What is the difference in thickness of the soap film from one band to the next?
A. 600 nm
B. 438 nm
C. 300 nm
D. 219 nm
E. 900 nm
13. A thin film of magnesium fluoride (n = 1.38) is applied to glass (n = 1.50) at a thickness of 100 nm. For
what visible wavelength will this coating act as nonreflecting?
A. 600 nm
B. 578 nm
C. 552 nm
D. 504 nm
E. 491 nm
15. What minimum thickness of oil (n = 1.50) on the surface of water (n = 1.33) would give destructive
interference for 550 nm light with normal incidence?
A. 275 nm
B. 183 nm
C. 92.0 nm
D. 80.0 nm
E. 78.0 nm
17. Laser light of 589 nm wavelength is shown through parallel slits forming a series of maxima on a screen
4.20 m away. If the distance between the central maximum and the first order maximum is 1.67 cm, what is the
slit separation?
A. 3.90 × 10-3 cm
B. 3.98 × 10-3 m
C. 9.98 × 10-5 m
D. 1.40 × 10-3 m
E. 1.48 × 10-4 m
18. In a Young's double slit experiment, a 5th order maximum occurs at an angle of 1.422°. If the screen is 3.90
m from the slits and the slit separation is 0.135 mm, what wavelength is being used?
A. 335 nm
B. 670 nm
C. 335 nm
D. 589 nm
E. 690 nm
24. In a double-slit interference pattern, the third maximum from the central maximum corresponds to which
value of m?
A. 1
B. 2
C. 3
D. 4
E. 5
25. Increasing the wavelengths in a double-slit experiment has what effect on the position of maxima on a
screen at fixed distance?
A. none
B. Maxima get closer together.
C. Maxima get farther apart.
D. Maxima get cancelled by minima.
E. Maxima pass minima on the screen.
27. A Young's double-slit experiment is performed and then repeated after moving the screen to triple the
previous distance from the slit. What happens to the angular separation (as measured from the slits) of the 4th
order maxima?
A. There is no change.
B. It becomes one-third the original value.
C. It becomes four times the original value.
D. It triples.
E. It increases by a factor of 2.25.
34. A single slit of width 0.030 mm is used to project a diffraction pattern of 500 nm light on a screen at a
distance of 2.00 m from the slit. What is the width of the central maximum?
A. 1.7 cm
B. 3.3 cm
C. 6.7 cm
D. 1.5 mm
E. 3.0 mm
35. A single slit of width 0.0300 mm is used to project a diffraction pattern of 500 nm light on a screen at a
distance of 2.00 m from the slit. What angle does the central maximum subtend as measured from the slit?
A. 1.91°
B. 3.82°
C. 0.945°
D. 1.50°
E. 3.00°
37. When the slit width is doubled, what happens to the width of the central maximum in the diffraction
pattern?
A. Nothing.
B. It doubles.
C. It halves.
D. It quadruples.
E. It quarters.