Monday, 20 October 2014


  1. There are two metal plates A and B in a glass tube. The air in the tube has been mostly pumped out. When a 470 nm light shines on A, a voltage is measured across AB. What is the colour of this light?
  2. Why does a voltage appear across AB? If we think of this as a cell, which plate is the positive pole?
  3. Find the frequency of the light. Find the energy of each of its photons.
  4. It takes at least 2.28 eV to remove an electron from metal A. What is the name of this energy?
  5. An electron absorbs the energy of one of the photons and jumps out of the metal plate. What is the range of possible energies of this electron?
  6. Why do the emitted electrons not all have the same energy?
  7. If A and B are connected by a piece of wire, a current flows. I want to connect a battery in the reverse direction to A and B to stop this current. What voltage must I use?
  8. What do you think the voltage in (ii) above might be? Why?