Physics 2.2.1-2: Photoelectric Effect and Collisions

21 flashcards · Physics · by TheoTyson

1. Describe the photoelectric effect

   When photons with enough energy collide with the surface of a metal, the electrons can be liberated from the surface.

2. What is the threshold frequency?

   The minimum frequency required to liberate any electrons from the surface.

3. What is the work function?

   Minimum energy required to liberate a photoelectron from the surface of the metal. (Property of the metal)

4. What is the maximum kinetic energy Ek(max)E_{k (max)}Ek(max)​ ?

   The maximum kinetic energy of all of the the photoelectrons that are released.

5. What is the stopping potential?

   The stopping potential required to stop any electrons reaching the collector electrode.

6. What happens when photons with a frequency lower than the threshold frequency are incident on a surface?

   The photons will not have enough energy to liberate any electrons even if the intensity is very high.

7. What happens when photons with a frequency higher than the threshold frequency are incident on a surface?

   The photons will have enough energy to liberate the electrons, and the energy left over is the energy of the photoelectron.

8. What is the effect when the amplitude of light is increased?

   The electric current will increase, but the kinetic energy of of the photoelectrons will remain the same. (More photoelectrons are liberated)

9. What is the effect when the frequency of the incident photons increases?

   The kinetic energy of the photoelectrons will increase, but the electric current will remain the same.

10. What is the photoelectric equation?

    hfhfhf === ϕ\phiϕ +++ Ek (max)E_{k {\ (max)}}Ek (max)​

11. Explain why the photoelectrons will have a range of kinetic energies.

    Electrons deeper in the metal require more energy to be liberated, and so the kinetic energy is less.

12. What is the equation for stopping potential and Ek(max)E_{k (max)}Ek(max)​ ?

    Ek(max)E_{k (max)}Ek(max)​ = VsV_sVs​ x 1.61.61.6 x 10−19C10^{-19}C10−19C

13. What are the three conclusions of the photoelectric effect?

    No photoelectrons are emitted if the photon frequency is below the threshold frequency. The photoelectrons are emitted with a variety of kinetic energies from zero to a maximum value that is dependent on the frequency of light. The number of photoelectrons emitted per second is proportional to the intensity of light.

14. What are ions?

    Charged atoms, the number of protons and electrons is not equal.

15. What is excitation?

    If electrons absorb a photon with the exact energy difference between two levels, then the electron can move up to a higher energy level.

16. What is the ground state?

    The lowest energy level possible around an atomic nucleus.

17. What is an electronvolt?

    The kinetic energy carried by an electron after it has been accelerated through a potential difference of 1V.

18. Why are photons only emitted with certain values?

    Electrons in atoms only exist in discrete energy levels, and when they move between them, they emit photons with the difference of energy.

19. What is ionisation?

    When an electron escapes its ground state and is removed from the atom.

20. What is the ionisation energy of an atom?

    The amount of energy needed to completely remove an electron from the atom from the ground state.

21. Describe how fluorescent tubes work

    An electric current is passed through a fluorescent tube containing mercury. This causes some of the free electrons to collide with mercury atoms and exciting them. This state is unstable, and so they move back down and release photons in the UV range. The UV photons excite the electrons in the phosphor coating so they move to an excited state. This state is unstable, and so they move back down and release photons in the visible light range.