C FOR DE
Max Planck theorized that energy was transferred in
chunks known as quanta, equal to hv. The variable h is a
constant equal to 6.63 x 10 J-s and the variable v
represents the frequency in 1/s. This equation allows us to
calculate the energy of photons, given their frequency. If
the wavelength is given, the energy can be determined by
first using the wave equation (c = λxv) to find the
frequency, then using Planck's equation to calculate energy.
Problem Solving Strategy
Known
Frequency (v)
Wavelength (2) v-
Energy (E)
v-
find the frequency. c=λxv
find the energy:
E=hv
E=hxv
Frequency (v)
Frequency (v)
c=λxv
E=hxu
1m = 1 x 10 nm
E-hv
[=>
example
Light with a wavelength of 525 nm is green. Calculate the energy in joules for a green light photon.
V=
useful equations
3.00x10 m/s
I m
1x10 m
E=(6.626x10J-s)(5.71x10 1/s)
-Wavelength (2)
525 nmx-
c=3.00 x 10 m/s
h=6.63 x 1034 J.s
1 kJ = 1000 J
Unknown
Energy (E)
Energy (E)
v=5.71x10 1/s
E-3.78x10JI photon
Use the equations above to answer the following questions.
1. Ultraviolet radiation has a frequency of 6.8 x 10¹5 1/s. Calculate the energy, in joules, of the
photon.
2. Find the energy, in joules per photon, of microwave radiation with a frequency of 7.91 x 10¹⁰ 1/s.
3. A sodium vapor lamp emits light photons with a wavelength of 5.89 x 107 m. What is the energy
of these photons?
4. One of the electron transitions in a hydrogen atom produces infrared light with a wavelength of
7.464 x 10 m. What amount of energy causes this transition?
5. Find the energy in kJ for an x-ray photon with a frequency of 2.4 x 10¹ 1/s.
6. A ruby laser produces red light that has a wavelength of 500 nm. Calculate its energy in joules.
7. What is the frequency of UV light that has an energy of 2.39 x 10¹ J?
8. What is the wavelength and frequency of photons with an energy of 1.4 x 10²¹ J?