## Quantum Physics

## Photoelectric Effect

The

**photoelectric effect**is when**photons**hit a metal passing its energy into the**delocalised electrons**removing them from the electrostatic forces holding them in the metal. As a photon is a quantum packet of energy as it passes its energy on it no longer exists. Only**high frequencies**carry enough energy to overcome the**work function**of the metal - this is called the**threshold frequency**. However the**intensity**of the light makes**no difference**as only**one photon can hit an electron**so the energy of each electron doesn't change just the amount of electrons being released increases.A

When a

To get rid of this negative charge

By removing the charge the gold leaf is

**gold leaf electrosope**is used to show the photoelectric effect.When a

**negative charge**is put through the apparatus then the gold leaf is**repelled**from the metal bar as they have the same charge.To get rid of this negative charge

**UV light**can be shone on the metal cap and this removes the excess electrons.By removing the charge the gold leaf is

**no longer repelled**so returns to the side of the metal bar.## Einstein's Photoelectric Effect Equation

This is why Einstein won the Nobel Prize

**Φ**is the**work function**energy. The minimum energy required to release an electron from the metal**Ek**is the**kinetic energy**the electrons have**after leaving**the metal. This gives how much energy the light is carrying and also enables the frequency to be worked out**E = hf = Ek + Φ**

## Energy of a photon

A photon is a

**quantum packet of energy**. The energy is measured in**eV**(electronvolts)**1eV = 1.6 x 10^-19 J**

The energy of a photon can be worked out by multiplying the frequency by the Planck's Constant which was created by one of the pioneers in Quantum Physics.**Energy (J) E = hf Planck's Constant (J/s) x frequency (Hz)**

Planck's constant isPlanck's constant is

**6.63 x 10^-34 J/s or 4.14 x 10^-15 eV/s**

**Top Tip:**In an exam they might ask you__hit a surface in one second - remember that__**how many photons****- find the**__Hertz means per second__**frequency**## Wave-Particle Duality

**De Broglie**discovered that all fundamental particles act like a wave as well as a particle

The equation below shows how the wavelength of light is related to the mass of a photon

In an exam the definition is the equation in words

**λ =**

__h__**mv**

**Wavelength =**

__Plancks constant__**momentum**

*The masses of the fundamental particles are given in the formula booklet*## Speed of Light

All electromegnetic waves travel at

The speed is directly proportional to the frequency of the wave and wavelength

This is used for electrons not photons though

For electromagnetic waves this means

The energy of a photon can also be deduced with the speed and wavelength of it (linking in with wave-particle duality)

**300'000'000 m/s**The speed is directly proportional to the frequency of the wave and wavelength

**v = fλ**This is used for electrons not photons though

For electromagnetic waves this means

**c = f****λ****c**stands for the**speed of light**The energy of a photon can also be deduced with the speed and wavelength of it (linking in with wave-particle duality)

**E =**__hc__**λ**## Energy Levels

Atoms have energy levels.

These are discrete levels where an electron can sit.

In an exam they'd give you the levels with corresponding energy values. These mean how much energy is required to remove the electron from the atom from that energy level. Ground level always has the lowest highest value.

When an electron

When an electron

These are discrete levels where an electron can sit.

In an exam they'd give you the levels with corresponding energy values. These mean how much energy is required to remove the electron from the atom from that energy level. Ground level always has the lowest highest value.

When an electron

**moves out**of an atom it**absorbs energy**- this can be**absorbed from a photon**When an electron

**moves down**energy levels it**releases energy**in the form of a**photon**. The light produced depends on how much energy is given off thus**E = hf**and**E=hc/****λ****becomes useful**## Line Spectra

A line spectra is a display of the wavelengths/frequencies emitted from a light source