7. Explain the relative health hazards of light waves, ultraviolet radiation, and x rays, in terms of the relative energy per photon.

8. From the use of cesium metal in photoelectric devices, would you expect Cs to have a larger, or smaller, first ionization energy than lithium and aluminum?

9. When cesium metal is used in a photocell in an automatic door opening circuit, what happens to the electrons that are knocked out of the cesium metal? How does the cesium ultimately get electrons back again? Does the signal.from the photocell circuit hold the door closed, or hold it open?

10. The voltage output of a photocell is proportional to the energy of the electrons ejected from the metal target. In contrast, the current output is proportional to the rate at which electrons are emitted from the target. What happens to the voltage of the photocell when the intensity of light falling on it is doubled? What happens to the current?

11. What happens to the voltage and current from the photocell when light of shorter wavelength but the same intensity as Question 10 is used?

12. How do your answers to the two previous questions provide evidence for the particle nature of light?