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B. The particulate nature of matter
B.2 Global warming
Steps
Worked example
Practice 1
Practice 2
Read the question carefully.
What is the power emitted by the Sun,
assuming it is a black body? It has a
temperature of 5 527
o
C and a radius of 7
x 10
8
m. The Stefan-Boltzman constant is
5.67 x 10
-8
W m
-2
K
-4
.
What is the albedo of the Earth if it
has 340 W m
-2
total incident power
but scatters 100 W m
-2
?
The average solar intensity at a solar panel
is 650 W m
-2
. The solar panel has an area
of 220 m
2
. If the solar panel is 100 %
effi cient, what is the power generated?
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
P = ?
T = 5 527
o
C
r = 7 x 10
8
m
σ = 5.67 x 10
-8
W m
-2
K
-4
.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
P = ?
T = 5 527
o
C = 5 800 K
r = 7 x 10
8
m
A = 4
𝛑
r
2
=
4
𝛑
x (7 x 10
8
m)
2
= 6.2
x 10
18
m
2
σ = 5.67 x 10
-8
W m
-2
K
-4
.
Write down the equation that links
the variables together
P = e σ
AT
4
Rearrange the equation to make
the unknown the subject
P =
σ
AT
4
Substitute your data into the
equation, including the units
P =
5.67 x 10
-8
W m
-2
K
-4
x 6.2 x
10
18
m
2
x (5 800 K)
4
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
P =
4 x 10
26
W
This is a constant
B. The particulate nature of matter
B.2 Global warming
Steps
Practice 3
Practice 4
Practice 5
:
write your own
Read the question carefully.
What is the peak wavelength fo
the Sun if it has a surface
temperature of 5 800 K?
What is the average temperature
of the Earth if it emits
2 x 10
17
W
of power. Radius of Earth is 6.3 x
10
6
m.
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
Write down the equation that links
the variables together
Rearrange the equation to make
the unknown the subject
Substitute your data into the
equation, including the units
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
