Physics 208, Spring 08, Week 12 Quizzes
1. Multiple choice
1. The Earth is about 1.49 x 108 km from the Sun. If the solar radiation at the top
of the Earth’s atmosphere has an intensity of 1340 W/m2, what is the total power
output of the Sun?
a. 7.10 x 1027 W
b. 2.20 x 1030 W
c. 6.62 x 1026 W
d. 3.74 x 1026 W
[Hint: assume isotropical radiation emission from the Sun in order to calculate the
area of a sphere at a distance equal to the Earth-Sun distance.]
Solution d)
I = P/A
Assuming isotropical emission A = 4πR2
P = IA, with R distance Earth – Sun.
2. If the radiant energy from the Sun comes in as a plane EM wave of intensity
1340 W/m2, calculate the peak values of E and B.
a. 300 V/m, 10-4 T
b. 1005 V/m, 3.35 x 10-6 T
c. 225 V/m, 1.6 x 10-3 T
d. 111 V/m, 3 x 10-5 T
Remember that ε0 = 8.85 x 10-12 C2/ (N m2). You can then derive μ0 if you do not
remember it…
Solution: b
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Emax = 1005 V/m
Bmax = 3.35e-6 T
3. Find the force exerted by reflecting sunlight off a perfectly reflecting
aluminium sheet in space if the area normal to the sunlight is 10000 m2 and
the solar intensity is 1350 W/m2.
a. 0.72 N
b. 0.09 N
c. 9 N
d. 45 N
Solution b)
Prad = 2Save/c=2I/c
F = Prad A = 0.09 N

4) Three linear polarizers are arranged as shown, with transmission axes
indicated by the thick solid line. The incoming light is circularly polarized, it is
propagating in the z-direction and the magnitude of the electric field vector
is E o . The electric field vector of the linearly-polarized light in region 1 has an
oscillating electric field vector with amplitude (maximum value) of E1 . What is
the ratio E1 / E o ? Explain.
y

x

30
˚
Circularly
polarized
light
z
90
˚
Region 1
Region 2
E1 / E0 
Region 3
Value
Solution: Polarizer 1 passes the y-component of the circularly polarized light. The
y-component has magnitude Eo, since whenthe rotating electric field of the
circularly polarized light points along the y-axis, there is no x-component, only y.
The y-component oscillates up and down, and has a maximum value of E o. so
the ratio E1 / Eo 1
