The photoelectric effect

Question 1

What is the Photoelectric effect?

Answer 1

It is where you shine radiation of a high enough frequency (above the work function) onto the surface of a metal that it emits photoelectrons. This is because of the way the atoms are bonded. Free-electrons are able to move about the metal, it is these electrons that absorb energy from the radiation, causing them to vibrate, break they bonds and escape the metal.

Question 2

What are the four conclusions drawn from the Photoelectric effect?

Answer 2

1. No electrons are emitted if the radiation has a frequency below the threshold frequency
2. The value of the maximum kinetic energy increases with the frequency of radiation.
3. The maximum kinetic energy of the photoelectrons emitted is unaffected by the intensity of the radiation.
4. The number of photoelectrons emitted per second is proportional to the intensity of the radiation.

Question 3

Define the threshold frequency.

Answer 3

The threshold frequency is the minimum frequency of light where photoemission still happens.

Question 4

What is the photon model of light?

Answer 4

It is where photons of light are perceived as having a one-on-one particle interaction with an electron in a metal surface, where each photon would transfer all its energy to one specific electron. It can be used to explain the photo electric effect.

Question 5

What is the equation for the energy of a photon?

Answer 5

E = hf = hc/λ

Question 6

Define the work function.

Answer 6

The minimum energy needed to emit electrons from a metal surface.

Question 7

What is the equation linking the threshold frequency and work function?

Answer 7

fo = ϕ/h

Question 8

Why do some electrons not have the maximum kinetic energy when emitted by photoemission?

Answer 8

Some electrons don’t have the maximum kinetic energy because some electrons are emitted from below the surface of the material so will have already lost some of the kinetic energy while escaping the material.

Question 9

What is the equation for the maximum kinetic energy of an emitted electron?

Answer 9

hf = Φ + Ekmax

Question 10

Explain what would happen if the intensity of the light is doubled.

Answer 10

The number of incident photons would double and so the number of emitted electrons would also double.

Question 11

Explain what would happen if the frequency is decreased.

Answer 11

1.) The frequency of the incident photon would be below the threshold frequency and so no electrons would be emitted. OR 2.) The energy of the photon depends on the frequency. If the frequency is decreased, then the photoelectrons would be emitted with a lower kinetic energy.