# Physics - Recall for Chapter 13: Quantum Physics

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-13-quantum-physics/ · Updated: 2021-08-03 · Tags: physics, school, quantum-physics, recall-questions

## Recall Questions
##### What is a photon??
A quantum of energy of electromagnetic radiation.

##### What is the photoelectric effect??
The emission of electrons from a metal surface when illuminated with light.

##### What is a photoelectron?
An electron that has been removed from a metal by absorbing a photon.

##### What is the work function??
The minimum energy required to release an electron from the surface of a metal.

##### What is the threshold frequency??
The minimum frequency of light required to produce photoelectrons from a metal.

##### What is monochromatic light??
Light of a single frequency/wavelength.

##### What is required for a photon to be able to produce photoelectrons??
Its frequency is greater than the threshold frequency.

##### Why can't light sources below the threshold frequency produce photoelectrons??
The photon eneergy is less than the work function.

##### How do photons and electrons interact??
A signle photon can be absorbed/emitted by a single electron which gains/loses the energy of the photon.

##### What is the effect on an electron of absorbing a photon??
The electron gains the energy of the photon.

##### What effect does increasing the frequency of a monochromatic light source have on photoelectrons produced??
Photoelectrons will have a greated maximum kinetic energy.

##### What is the effect of increasing the intensity of a monochromatic light source on photoelectrons produced??
More photoelectrons will be produced but they will have the same maximum kinetic energy.

##### What two factors determine the maximum kinetic energy of photoelectrons??
The frequency of the light and the work function of the metal.

##### What is $KE_\text{max}$ in Einstein's photoelectric effect equation ($hf = \phi + KE_\text{max}$)??
The maximum kinetic energy of the photoelectrons.

##### According to the wave model, how is energy transferred from light to electrons in a metal??
It is delivered continuously and builds up over time.

##### If light is above the threshold frequency, how long will it take for photoelectrons to start being produced??
It is instantaneous.

##### What happens if very intense light that is below the threshold frequency is used??
No photoelectrons are produced, regardless of intensity.

##### What determines the energy of a photon??
The frequency/wavelength.

##### How do you calculate the energy of a photon??
$$E = hf$$ or $$E = \frac{hc}{\lambda}$$

##### What is an electron volt??
The energy gained or lost by an electron passing through a potential difference of $1V$.

##### What is the threshold p.d. of an LED??
The minimum potential difference required for the LED to produce light.

##### How can the threshold p.d. of an LED be used to find photon energy??
The energy transferred by the electrons ($eV$) is equal to the energy of the photons produced ($hf$).

##### What is meant by wave-particle duality??
It describes how all matter can display both wave and particle properties.

##### What is the key piece of evidence for wave-particle duality??
When an electron beam passes through polycrystaline graphite, it produces a diffraction and interference pattern.

##### What is the relationship between momentum and wavelength??
Inverse proportionality.

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