3.2.2 Electromagnetic radiation and quantum phenomena

Page 1

The photoelectric effect

When photons collide with a metal, they can cause free electrons to be emitted from the surface of the metal.

One photon interacts with one electron.

If the photon has enough energy (threshold frequency of the metal) then the electron will be emitted

This is represented by the equation:

φ, the Greek letter phi, represents the work function.

if the work function is not met, then no electrons will be emitted.

As long as the work function is met, the number of electrons emitted increases with light intensity.

A photoelectric emitter can be connected to a circuit used to create a current.

This is how solar panels work.

Stopping potential is the minimum pd that must be put through the circuit to prevent electrons from crossing the gap

in these cases, we call the emitter a cathode since it gives out electrons.

Page 2

Collisions of electrons with atoms

When electrons collide with atoms, energy can be transferred to one of the electrons in the atom.

This can cause:

excitation

if enough energy is transferred, then an electron can move up to a higher energy level.

Ionisation

if even more energy is transferred then the electron can leave the atom entirely causing ionisation.

The electron volt is the energy required to move a single electron through a potential difference of one volt.

it is the equivalent of 1.6 * 10^-19 Joules

Page 3

Energy levels and photon emission

When electrons move to a lower energy level, they emit energy in the form of light.

Each element has different energy levels and therefore emits different frequencies of light.

We can use line spectra to identify elements because of this.

Page 4

Wave-particle duality

Electron diffraction suggests that particles can show wave-like properties.

The photoelectric effect suggests that waves can show particle-like properties.

The de Broglie wavelength:

This is used to calculate the wavelength of a particle.

Because the wavelength varies based on momentum, the wave-like properties exhibited by particles are also affected by momentum

As new experiments prove current theories and models to be incorrect scientists have to adapt them to allow for the new knowledge.

This leads to our understanding of matter changing over time.

However such changes only occur after the community has reviewed findings.