# Energy and Light

advertisement ```Energy and Light – Honors Chemistry
Values and equations:
E= hν
c= λν
λ = h/mν
ν= [RH /h][1/ni2 – 1/nf2]
Name: ___________________
RH = 2.18 x 10-18 J h= 6.626 x 10-34 J&middot;s
Show ALL work for the following problems.
1. The rays from the sun that cause tanning and burning are in the UV portion of the electromagnetic
spectrum. UV – A radiation has wavelengths in the range of 320 – 380 nm, while UV – B rays have
wavelengths in the 290 – 320 nm.
(a) Calculate the frequency of light with a wavelength of 320. nm?
(b) Calculate the energy of a photon with the frequency calculated in (a).
(c) Calculate the energy of a mole of photons with a wavelength of 320. nm.
(d) Which photons have more energy UV – A or UV – B?
(e) UV – B radiation from the sun is considered a greater cause of sunburn in humans than is UV – A.
Use the information in the problem to explain why.
2. The distance between the Mars and Earth when they’re both on the same side of the sun is
approximately 5.46 x 107 km.
a. How long would it take a radio wave with a frequency of 7.25 x 105 Hz to travel from Mars to Earth?
b. How long would it take gamma radiation with a wavelength of 0.80 pm to reach Earth from Mars?
3. Cobalt – 60 is an artificial radioisotope that is produced in a nuclear reactor for use as a gamma-ray
source in the treatment of certain types of cancer. If the wavelength of the gamma radiation from a cobalt –
60 source is 1.00x 10-3 nm, calculate the energy of a photon of this radiation?
4. A laser emits light with a frequency of 4.69 x 1014 Hz. What is the energy of one quantum of this energy?
The laser emits energy in pulses of short duration. If the laser emits 1.3 x 10-2 J of energy during a pulse,
how many quanta of energy are emitted during a pulse?
5. Use the de Broglie relationship to determine the wavelengths a lithium atom moving at 2.5 x 105 m/s. (1
amu = 1.66053886 &times; 10-24 grams)
6. For each of the following electronic transitions, is energy emitted or absorbed?
a.
From n = 4 to n = 2
b. From an orbit of a radius
2.12 &Aring; to one of a radius of
8.48 &Aring;.
c. From n = 6 to n = 9
7. Complete the chart below and SHOW ALL WORK.
ni
5
nf
4
2
E
6
7.57 x 10-20 J

95.0 nm
Absorbed
or emitted?
λ
(d) Do any of these transitions emit or absorb light in the visible part of the spectrum? If so, which ones?
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