April 2, 2009
PHY 2054 Discussion Spring ‘09
Conceptual Review: Chapter 22
A . Nature of Light
1.
If you double the wavelength of a monochromatic light, by what factor does the energy content of
individual photon change?
2. Express the minimum angular frequency in Fizeau’s experiment in terms of
speed of light, # of teeth N and distance d.
B. Reflection & Refraction
1. Two mirrors meet at a right angle. A beam of light strikes one of the mirrors at an angle of 20º from the
normal. What is the angle of reflection after it is reflected from both mirrors.
2. A monochromatic light is incident on an air-water interface. Compare the velocity, frequency and
wavelength in air and those in water.
4. A beam of light both reflects and refracts at the air-glass surface. What is angle
of incidence that would result in the reflected and refracted rays being
perpendicular to each other?
C. Dispersion
1. Does the index of refraction increase/decrease with increasing frequency?
2. The index of refraction for red light in water is 1.331 and that for blue light is 1.340. If a ray of white
light is incident onto a water surface from air, what is the maximum angle of between the red and blue
components of the light?
D. Total Internal Reflection,
1. A light ray is incident on an air-water boundary from the air. Does the total internal reflection occur?
2. A ray of light is incident on the end of a transparent pipe. What is the
maximum angle of incidence for the light to transmit in the pipe?
April 2, 2009
PHY 2054 Discussion – Spring ‘09
Practice Exam Problems (Chapter 22)
1. Photon A has an energy of 2.0  10-19 J.
Photon B has 4 times the frequency of Photon A.
the energy of Photon B? (Energy of Photons)
a. 0.50 10
-19
J
b. 1.0 10
-19
J
c. 8.0 10
-19
What is
J
d. 32
10-19 J
2. If the wavelength of a monochromatic source is 490 nm in vacuum, what is the wavelength from the
same source when it passes through a liquid where the speed of light is 2.40  108 m/s? (c = 3.00  108
m/s) (Index of Refraction)
a. 671 nm b. 612.5 nm c. 490 nm d. 392 nm
3. An oil film floats on a water surface. The indices of refraction for water and oil, respectively, are 1.333
and 1.466. If a ray of light is incident on the air-to-oil surface at an angle of 37.0º with the normal, what is
the angle of the refracted ray in the water? (Snell’s Law)
a. 18.1 º
b. 24.2 º
c. 26.8 º
d. 37.0 º
4. A certain kind of glass has nblue = 1.650 for blue light and nred = 1.610 for red light. If a beam of white
light (containing all colors) is incident at an angle of 30.0º, what is the angle between the red and blue
light inside the glass?
(Dispersion)
a. 0.22 º
b. 0.45 º
c. 1.90º
d. 1.81 º
5. When light of one wavelength from air hits a smooth piece of glass at an angle, which of the following
will not occur? (Conditions for Dispersion)
a. reflection
b. refraction
c. dispersion d. All of the
above will occur.
6. A small underwater pool light is 1 m below the surface of a swimming pool. What is the radius of the
circle of light on the surface, from which light emerges from the water? (nwater = 1.333). (Total Internal
Reflection )
a. 0.57 m b. 0.77 m c. 1.13 m d. 1.43 m
7. A fiber optic cable (n = 1.50) is submerged in water (n = 1.33). What is the critical angle for light to
stay inside the cable?
Answers: 1-c
2-d
(Optical Fibers)
3-c
4-b
5-c
6-c
a. 83.1º
7-b
b. 62.5 º
c. 41.8 º
d. 27.6 º