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Period 3 Exercise Answers
E.1
An electron absorbs a photon that has 5.0 x 10
–21
joules of energy and the electron moves to a
higher energy level.
The electron later drops to
a lower energy level and emits a photon that has
3.3 x 10
–22
joules of energy.
How much more
energy must be emitted to satisfy conservation
of energy?
a)
1.7 x 10
–22
joules
b)
4.7 x 10
–22
joules
c)
1.7 x 10
–21
joules
d)
4.7 x 10
–21
joules
e)
4.7 x 10
–20
joules
The total energy emitted by the electron must
equal the total energy absorbed.
Subtract to
find the difference between the energy
absorbed and the energy emitted.
When
adding or subtracting numbers in scientific
notation, each term must have the same power
of ten.
5.0
x 10
–21
J
5.0
x 10
–21
J
– 3.3
x 10
–22
J
=
– 0. 33 x 10
–21
J
4.7
x
10
–21
J
Or
5.0
x 10
–21
J
50.0
x 10
–22
J
– 3.3
x 10
–22
J
=
– 3. 3
x 10
–22
J
46.7
x 10
–22
J = 4.7 x
10
–21
J
E.1
=
d
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The part of the electromagnetic spectrum
that causes tanning is
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 Winter '11
 Staff
 Energy, Photon

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