ATOC/ASEN 5235
Midterm Exam
8 October 2009
All problems are worth 10 points
Problem 1
.
What are the three main processes by which the atmosphere interacts with
radiation?
Answer
:
Emission, Scattering, Absorption
Problem 2
:
A particular light bulb emits radiation at a wavelength of 500 nm with a
power of 10 W.
How many photons are emitted each second?
Solution:
Energy of one photon = E = hc/
λ
.
Since 1 W = 1 J s
1
:
h = 6.625x10
34
Js
c = 3.0x10
8
ms1
λ
= 5.0x10
7
m
hc/
λ
= 3.98x10
19
J
# photons per second = 2.51x10
19
Lots of photons!!
Problem 3
: In class on 20090903, we derived the equation F =
π
L, where F is the
irradiance (W m
2
) and L is the radiance (W m
2
sr
1
). Explain the assumption(s) involved
when using this equation. That is, when is it appropriate to use F =
π
L? I am looking
only for a single sentence.
Answer:
Only if the radiation field is isotropic, and we are considering only the
hemispheric
irradiance (that is, we integrated over a single hemisphere, not over
4
π
sr).
Problem 4.
Give an estimate for the solar irradiance at the top of the atmosphere of Mars.
Answer
:
The solar irradiance at Earth is 1361 W m
2
.
We can use the inverse
square law to calculate the irradiance at Mars.
Since the EarthSun distance is 1
AU, and the MarsSun distance is 1.524 AU, the irradiance at Mars is 1361 x
(1/1.524)
2
= 586 W m
2
.
λ
/
photon
1
Js
10
photons
#
1

hc
s
⋅
×
=
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View Full DocumentProblem 5
: Why do diamonds sparkle, often looking like a whole suite of tiny prisms?
Answer:
This is essentially problem 1 from homework #4. The basic reason is
that the critical angle for a diamond/air interface is only 24°.
The average index of refraction for diamond in the visible region of the spectrum
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 Fall '10
 Randell
 Light, Tfood, warm food

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