PHYS 252 TEST #3 02/27/08 Dr. Holmes NAME
ANSWER ALL 9 QUESTIONS. THE WORTH OF EACH PART OF EACH QUESTION IS CIRCLED NEAR THE PLACE FOR THE ANSWER. SHOW YOUR WORK ON PROBLEM TYPE QUESTIONS, AND ANSWER BRIEFLY BUT TO THE POINT ON WORD QUESTIONS.
1) The sun's radiation peaks at a wavelength of 480 nm. The sun has a radius of 700,000 km (recall surface area of a sphere is 4p r2 ).
a) Assuming the sun is a perfect blackbody, what is the surface temperature of the sun?
6042 K.
b) How much total power does the sun emit (in Watts) ?
4.65 x 1026 Watts.
Mars is 228 million kilometers (143 million miles) away from the sun.
c) What is the power per area from the sun on Mars at Mars’ distance from the sun (in Watts/m2) ? This answer is for a solar receiver above Mars’ atmosphere pointing directly at the sun.
712 W/m2.
2) a) Show using a graph of intensity vs wavelength what happens experimentally in blackbody radiation:
b) Show on the above graph using a dotted line what the classical (wave) theory predicted for blackbody radiation.
c) What did Planck do differently from the classical wave theory to predict the actual behavior of blackbody radiation?
3) PHOTOELECTRIC EFFECT:
a) Draw a diagram showing the experimental setup for the photoelectric experiment:
b) Describe one part of the experiment that cannot be explained by the wave theory. (A graph would help.)
c) Describe how the particle (photon) theory can explain the above part of the experiment.
d) If the work function for a metal is 2.8 eV, what is the cut-off frequency for light to eject photo-electrons from this metal?
6.76 x 1014 Hz.
e) What is the wavelength for this frequency of light?
444 nm.
f) Will light of wavelength 408 nm be able to eject electrons from the metal? If so, what is the stopping voltage for this light; if no, then answer N.A.:
Yes; 0.25 volts.
g) Will light of wavelength 632 nm be able to eject electrons from the metal? If so, what is the stopping voltage for this light; if no, then answer N.A.:
No; N.A.
4) a) What is the evidence against the plum pudding model of the atom? (Name and briefly describe the experiment):
b) What is the approximate size of an atom?
10-10 m.
c) What is the approximate size of the nucleus?
10-14 m.
d) What is the approximate size of the electron?
Less than 10-17 m.
5) a) What is the ground state energy of the hydrogen atom?
-13.6 eV = -2.18 x 10-18 J.
b) How much energy is emitted when the electron falls from the n=4 state to the n=2 state in the hydrogen atom?
2.55 eV.
c) What type of photon is this (e.g., ultraviolet, infrared, etc. (if visible, specify the color):
blue-green.
6) a) If there is such a thing as the DeBroglie wavelength, then we should be able to test it. Describe one experiment in support of the DeBroglie wavelength for matter.
b) Tell how the DeBroglie wavelength "explains" the Bohr assumption that L = nh .
7) a) What does the Heisenberg Uncertainty Principle say? (use an equation and identify all terms used)
b) Demonstrate this uncertainty by describing one experiment that tries to measure those quantities it relates.
8) a) State the Pauli Exclusion Principle?
b) Does it apply to all particles? (If NO, then indicate which it does apply to and which it does not apply to.)
c) Explain how the Pauli Exclusion Principle follows from the Heisenberg Uncertainty Principle and the Schrodinger Equation.
9) Explain the principles of a laser. In particular, explain what is meant by:
a) a metastable state
b) a population inversion
c) distinguish between stimulated and spontaneous emission: