Problem Set 4
Chapter 33: Electromagnetic Waves
Exercises & Problems: 2, 16, 33, 40, 46, 55, 60, 63, 76, 90
Question A
Explain in detail how electromagnetic waves can be created by an accelerating
electric charge using Maxwell’s equations.
Question B
When light waves enter a medium of higher refractive index than the previous,
why is it that (i) frequency stays the same? (ii) wavelength decrease?, and (iii)
speed decreases?
Question C
Using the dielectric model of the atom, explain why (i) glass is transparent for
optical frequencies but is opaque for UV and IR frequencies? (ii) How is light
transmitted through clear glass?
Question D
What I the difference between a mirror and a white sheet?
Question E
You pull out one polarizer (≡ A) and notice that some of the light is “block.” You pull out
a second polarizer (≡ B) and stack it on top of polarizer-A at the same angle of
polarization (assume A and B are identical). (i) Does polarizer-B stack on top of
polarizer-A block more, less, or same amount of light than polarizer-A by itself? Assume
a perfect polarizer. (ii) Re-answer the question (i) where the polarizer is now not perfect.
Problem 33.2
Project Seafarer was an ambitious program to construct an enormous antenna, buried
underground on a site about 10 000 km2 in area. Its purpose was to transmit signals to
submarines while they were deeply submerged. If the effective wavelength were 104
Earth radii, what would be the (a) frequency and (b) period of the radiations emitted?
Ordinarily, electromagnetic radiations do not penetrate very far into conductors such as
seawater, and so normal signals cannot reach the submarines.
Problem 33.16
Frank D. Drake, an investigator in the SETI (Search for
Extra-Terrestrial Intelligence) program, once said that the
large radio telescope in Arecibo, Puerto Rico, “can detect a
signal which lays down on the entire surface of the earth a
power of only one picowatt.” (a) What is the power that
would be received by the Arecibo antenna for such a
signal? The antenna diameter is 300 m. (b) What would be
the power of an isotropic source at the center of our galaxy
that could provide such a signal? The galactic center is 2.2
×104 ly away. A light-year is the distance light travels in
one year.
Problem 33.33
In the figure, initially unpolarized light is sent into a system of
three polarizing sheets whose polarizing directions make
angles of θ1 = 40°, θ2 = 20°, and θ3 = 40° with the direction of
the y axis. What percentage of the light’s initial intensity is
transmitted by the system? (Hint: Be careful with the angles.)
Problem 33.40
In the figure, unpolarized light is sent into a system of three polarizing sheets. The
angles 1, 2, and 3 of the polarizing directions are measured counterclockwise from the
positive direction of the y axis (they are not drawn to scale). Angles 1 and 3 are fixed,
but angle 2 can be varied. The figure gives the intensity of the
light emerging from sheet 3 as a function of 2. (The scale of
the intensity axis is not indicated.) What percentage of the
light’s initial intensity is transmitted by the three-sheet system
when 2 = 90°?
Problem 33.46
In figure (a), a light ray in an underlying material is incident at angle 1 on a boundary
with water, and some of the light refracts into
the water. There are two choices of underlying
material. For each, the angle of refraction 2
versus the incident angle u1 is given in figure
(b). The horizontal axis scale is set by 1S = 90°.
Without calculation, determine whether the
index of refraction of (a) material 1 and (b)
material 2 is greater or less than the index of
water (n = 1.33).What is the index of refraction
of (c) material 1 and (d) material 2?
Problem 33.55
In the figure, a 2.00-m-long vertical pole extends from the
bottom of a swimming pool to a point 50.0 cm above the water.
Sunlight is incident at angle  =55.0°. What is the length of the
shadow of the pole on the level bottom of the pool?
Problem 33.60
In Fig. 33-58, light from ray A refracts from material 1 (n1 = 1.60) into a thin layer of
material 2 (n2 =1.80), crosses that layer, and is then incident
at the critical angle on the interface between materials 2 and 3
(n3 = 1.30). (a) What is the value of incident angle θA? (b) If θA
is decreased, does part of the light refract into material 3?
Light from ray B refracts from material 1 into the thin layer,
crosses that layer, and is then incident at the critical angle on
the interface between materials 2 and 3. (c) What is the value
of incident angle θB? (d) If θB is decreased, does part of the
light refract into material 3?
Problem 33.63
In the figure, light enters a 90° triangular prism at point P with
incident angle θ, and then some of it refracts at point Q with an
angle of refraction of 90°. (a) What is the index of refraction of the
prism in terms of θ? (b) What, numerically, is the maximum value
that the index of refraction can have? Does light emerge at Q if the
incident angle at P is (c) increased slightly and (d) decreased
slightly?
Problem 33.76
In the figure, unpolarized light with an intensity of 25 W/m2 is
sent into a system of four polarizing sheets with polarizing
directions at angles θ1 = 40°, θ2 = 20°, θ3 = 20°, and θ4 =
30°.What is the intensity of the light that emerges from the
system?
Problem 33.90
In the figure, two light rays pass from air through five layers of transparent plastic and
then back into air. The layers have parallel interfaces and unknown thicknesses; their
indexes of refraction are n1 = 1.7, n2 = 1.6, n3 = 1.5, n4 = 1.4, and n5 = 1.6. Ray b is
incident at angle θb = 20°. Relative to a normal at the last interface, at what angle do (a)
ray a and (b) ray b emerge? (Hint: Solving the problem algebraically can save time.) If
the air at the left and right sides in the figure were, instead, glass with index of refraction
1.5, at what angle would (c) ray a and (d) ray b emerge?