Quantum Effects and Photons
What's the difference between a "red hot" poker and a "white hot" poker?
•
The pokers are different temperatures ("white hot" poker has a higher temperature)
•
The pokers emit different intensities and wavelengths of electromagnetic radiation
(especially in the visible spectrum
Max Planck (1900)
Energy can be released (or absorbed) by atoms only in "packets" of some minimum size
•
This minimum energy packet is called a
quantum
•
The energy (
E
) of a quantum is related to its frequency (
ν
) by some constant (
h
):
E = h
ν
•
h
is known as "
Planck's constant
", and has a value of
6.63 x 10
34
Joule seconds (Js)
•
Electromagnetic energy is always emitted or absorbed in whole number multiples of
(h*
ν
)
Calculate the smallest amount of energy (i.e. one quantum) that an object can absorb from
yellow light with a wavelength of 589 nm
Energy quantum = h
ν
so we need to know the frequency
ν
ν λ
= c
ν
= c/
λ
ν
= (3.00 x 10
8
m/s)/(589 x 10
9
m)
ν
= 5.09 x 10
14
s
1
plugging into Planck's equation:
E = (6.63 x 10
34
Js)*( 5.09 x 10
14
s
1
)
E (1 quanta) = 3.37 x 10
19
J
Note that a quanta is quite small. When we receive infrared radiation from a fireplace we absorb
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 Winter '11
 HECTORRODRIGUEZ
 pH, Energy, Photon, Light, Max Planck

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