Photoelectric effect

Question 1

What is the photoelectric effect?

Answer 1

electrons are emitted from the surface of a metal when electromagnetic radiation above a certain frequency was directed at a metal

Question 2

What new theory did Einstein create?

Answer 2

proposed that light it composed of wavepackets or photons each of energy equal to hf where h is the Planck contant (6.63x10^-34 where f is frequency

Question 3

How did Einstein say the photoelectric effect occurred?

Answer 3

electron on the metals surface absorbs a single photon from the incident light and gains energy equal to hf

Question 4

What is the work function of the metal?

Answer 4

the minimum energy needed by an electron to escape from the metal surface when the metal is at zero potential excess energy gained by the photoelectron becomes kinetic energy in the order of 10^-19J

Question 5

What is the stopping potential?

Answer 5

the minimum poteintial needed to stop photoelectric emission the electrons that escape can be attracted back by giving the plate a sufficient positive charge kinetic energy of the electron is reduced to 0 because the electron must do extra work

Question 6

Why do emitted electrons have a range of kinetic energies up to a maximum value?

Answer 6

energy of photon is constant electron has to overcome work function deeper electrons require more energy

Question 7

Explain why, when UV light is shone on a positively charged plate, no charge is lost by the plate?

Answer 7

process involves the ejection of negatively charged electrons

any electrons emitted will make the positive charge greater

Question 8

Why is E_k(max) a max in hf = θ + E_k(max)?

Answer 8

work function is the minimum amount of energy needed to remove an electron from the surface

the rest is kinetic energy

same energy absorbed

Question 9

How does photelectricity prove the particle like nature of lught?

Answer 9

light travels as particle

energy is in discrete packets

Question 10

How does threshold frequency support particle nature of EM waves?

Answer 10

• threshold freq minimum freq for emission of electrons
• if freq below the threshold freq no emission even if intensity increased
  
  • because energy of the phton is less than work function
• wave theory can not explain this as energy of wave increases with intensity
• light travels as photons that depend on freq
  
  • if freq above threshold, photon has eneough energy
• lack of time delay