Einstein

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Einsteins photon theory
Photons corpuscular theory E hf E Photon
energy (Joules) h Plancks constant 6.626 x
10-34 Js f frequency of oscillations (Hz,
s-1) v f? v c speed of light 3.00 x 108
m/s f frequency (Hz) ? wavelength (m)
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Example 1 What is the energy of a 460. nm
photon? 4.3213E-19 J, 2.70 eV
E hf, h 6.626E-34 Js v f? E Photon energy
(Joules) v c 3.00 x 108 m/s f frequency
(Hz) ? wavelength (m)
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Example 2 A photon has an energy of 13.6 eV.
What is its wavelength? (Remember V W/q, and 1
eV is one electron moved through 1 volt)
9.12371E-08 m 91.2 nm
E hf v f? E Photon energy (Joules) v c
3.00 x 108 m/s f frequency (Hz) ? wavelength
(m)
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Ex1 What is the energy (in J) of a photon with a
frequency of 6.58 x 1014 Hz?
E hf (6.626 x 10-34 Js)(6.58 x 1014 s-1)
4.36 x 10-19 J
4.36 x 10-19 J
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Ex2 - What is the wavelength of a photon with an
energy of 5.45 x 10-18 J?
E hf f E/h (5.45 x 10-18 J)/(6.626 x 10-34
Js) 8.23 x 1015 Hz v f?, ? v/f (3.00 x
108 m/s)/(8.23 x 1015 Hz) 3.65E-8 m 36.5 nm
36.5 nm
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Ex3 -What is the energy (in eV) of a 314 nm
photon?
E hf hc/? 1eV 1.602 x 10-19 J E hc/?
(6.626 x 10-34 Js)(3.00 x 108 m/s)/(314 x 10-9 m)
6.33 x 10-19 J E (6.33 x 10-19 J)/(1.602 x
10-19 J/eV) 3.95 eV
6.33 x 10-19 J, 3.95 eV
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A photon has an energy of 6.02 eV. What is its
wavelength? (answer in nm) (2)
E hf hc/? 1eV 1.602 x 10-19 J E (6.02
eV)(1.602 x 10-19 J/eV) 9.64 x 10-19 J E
hc/?, ? hc/E (6.626 x 10-34 Js)(3.00 x 108
m/s)/(9.64 x 10-19 J) 2.06 x 10-7 m 206 nm
(nm 1 x 10-9 m)
206 nm
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How many photons per second stream from a 620.
nm, 300. mW laser? (2)
E hf hc/? In one second, a 300 mW laser emits
photons with a total energy of .300 J E hc/?,
(6.626 x 10-34 Js)(3.00 x 108 m/s)/(620. x 10-9
m) 3.20613 x 10-19 J (per photon) photons
(.300 J/s)/(3.20613 x 10-19 J/photon) 9.36 x
1017 photons/sec Hey, thats a lot!
9.36 x 1017 photons/sec