Modern Physics Multiple Choice Help

Jun 2013
2
0
For these 4 questions I know the right answer, I just would like a quick explanation why. Thanks!

1) In which one of the following experiments would evidence arise to support deBroglie's matter-wave theory?
A: In diffracting a beam of electrons through a very small single slit.

2) In an experiment, light of a particular frequency is incident on a metal surface, and photoelectrons are emitted from the surface as a result. When the intensity of the light is increased, the experimenter notices that the number of photoelectrons per second ______, while the max kinetic energy of the photoelectrons _______.
A: increases, is unaffected

3. Quantum concepts are critical in explaining all of the following except...
A: the Compton effect

4. A nucleus of 210, 82 Pb undergoes alpha decay. Which one of the following statements is true about the decay products?
A: The daughter nucleus does not move as a result of the decay.
 

topsquark

Forum Staff
Apr 2008
3,106
659
On the dance floor, baby!
For these 4 questions I know the right answer, I just would like a quick explanation why. Thanks!

1) In which one of the following experiments would evidence arise to support deBroglie's matter-wave theory?
A: In diffracting a beam of electrons through a very small single slit.
Well, you can't diffract a beam of particles...

2) In an experiment, light of a particular frequency is incident on a metal surface, and photoelectrons are emitted from the surface as a result. When the intensity of the light is increased, the experimenter notices that the number of photoelectrons per second ______, while the max kinetic energy of the photoelectrons _______.
A: increases, is unaffected
I can't answer this quickly. But this is a reasonably good reference for the topic.

3. Quantum concepts are critical in explaining all of the following except...
A: the Compton effect
I'm not certain I agree with this, though obviously we don't have the other possible answers to compare. The Compton effect is the scattering of a photon (x-ray photon in this case) off an electron. Whereas this is a "simple" example of scattering, which can be treated as a particle collision, there is that little "h" in the formula...which is almost always a good indicator of the presence of Quantum Mechanics. In the spirit of things this process can be derived by Special Relativity, though the value of the constant h can only be measured rather than predicted.

4. A nucleus of 210, 82 Pb undergoes alpha decay. Which one of the following statements is true about the decay products?
A: The daughter nucleus does not move as a result of the decay.
I'm a bit skeptical about this one as well, but seeing as I don't have my decay table to hand I'm going to assume that the answer is correct and put out an idea for you to check.

When a parent nucleus (Pb in this case) decays into daughters (the alpha particle and Hg nucleus) are produced we expect to see motion when there is an energy difference on one side of the equation. In this case I suspect that you will find that the energy balance is the same on both sides of the equation, meaning that there is no energy left over to constitute a kinetic energy for either daughter product.

-Dan