PHYS 202 Test #4 4/17/09 Dr. Holmes NAME
DO ALL THE PROBLEMS. THE WORTH OF EACH PROBLEM IS MARKED BESIDE THE SPACE FOR THE ANSWER. SHOW YOUR WORK FOR PARTIAL CREDIT.
1) Assume the earth is a smooth sphere of radius 6,400 km, and assume it has a uniform surface temperature of 50oF.
a) Assuming the earth is a smooth sphere, what is the earth’s surface area?
5.15 x
1014 m2
b) What would be the earth’s power output radiated back into space (if it had no atmosphere) under the above assumptions?
1.87 x 1017 Watts
c) At what wavelength would the earth’s radiation peak?
1.02 x 10-5 m = 10.2
micrometers
d) What kind of radiation is this peak radiation (i.e., IR, UV, visible, etc.)?
IR
2) a) Describe one aspect of the photoelectric effect that contradicts what the wave theory of light predicts.
b) Indicate in which way it contradicts what the wave theory predicts.
c) Indicate how the particle (photon) theory accounts for the aspect:
3) a) Given that the work function of potassium is 2.2 eV, what is the cut-off frequency for the photoelectric effect with potassium?
5.3 x 1015 Hz.
b) What wavelength is associated with this cut-off frequency?
5.65 x 10-7m = 565 nm.
c) What is the stopping voltage required for ultraviolet light of wavelength 380 nm ?
1.07 Volts.
d) Will infrared light be able to eject electrons from this metal?
No.
e) Will blue light be able to eject electrons from this metal?
Yes.
4. a) List two experiments that indicate light behaves as a wave and not as a particle:
(1)
(2)
b) List two experiments that indicate light behaves as a particle and not as a wave:
(1)
(2)
5. a) What is the energy of a photon given off by a hydrogen atom in going from the n=3 state to the n=1 state?
12.09 eV = 1.93 x 10-18 J.
b) What is the wavelength of light from this transition?
1.03 x 10-7 m = 103 nanometers
c) What type (or if visible, what color) is this photon?
Ultraviolet.
6. a) Briefly explain how the DeBroglie wavelength idea is used to explain why electrons can exist in state n=1 or state n=2 but not in a state with n=1.66 .
b) Describe one experiment that supports the idea that an electron shows wave properties and has a wavelength equal to the DeBroglie wavelength.
7. a) How big is an atom (length in meters)?
10-10 meters (roughly).
b) How big is the nucleus?
10-14 meters (roughly).
c) How big is the electron?
Less than 10-18 m.
d) How do we know the above value for part b (size of nucleus)?
8. a) What is the speed of an electron accelerated through 9 volts?
1.78 x 106 m/s.
b) What is the momentum of this electron (at the above speed)?
1.62 x 10-24 kg*m/sec.
c) What is the wavelength of this electron (at the above momentum)?
4.10 x 10-10 m = 0.41 nm.
d) What is the wavelength of a photon that has an energy of 9 eV ?
1.38 x 10-7 m = 138 nm.
9. a) State the Heisenberg Uncertainty Principle:
b) Design an experiment to locate an electron, and show how this principle applies when you try to locate the position of that electron.
10. Explain the following terms as they are related to the operation of a laser:
a) spontaneous emission:
b) stimulated emission:
c) population inversion:
d) light amplification: