I have my final exam coming up on tuesday and I've been going over past examinations. I mainly have problems with E &M and the particle/wave nature of light. I have some questions that I wasn't able to answer myself that I was hoping people could help me out with. 1. Why does the photoelectric effect suggest that light has particle-like properties? Orange light can generate photoelectrons from the metal potassium, but red light cannot. Name another color of light which can produce the photoelectric effect in potassium and explain your answer. 2. Why do the magnetic field lines outside of an isolated bar magnet never cross? 3. What does the double slit experiment using electrons tell us about the wave and particle nature of electrons? 4. Can atoms ever be at rest? Answer this question from the point of view of classical and quantum mechanics. Think about cooling a gas of atoms to near absolute zero temperature. 5. What is the perihelion shift of the planet Mercury? How does the measurement of this quantity support the predictions of the General Theory of Relativity? for this last question, I know that the perihelion is the closest point of a planets orbit to the sun. I also know that the axis of perihelion shifts slowly over time. Basically I do not know why, and how it is related to general relativity. Thanks in advance for any help that can be offered.