1. Fluorescence and Electron Collisions
• What is the equation for the energy of a
photon relating to its frequency?
• What’s the name of the constant and what is
its value?
• What is the name we give to a particle of
light? What is different between this and a
wave of light?

2. Electron Collisions
Objective
• Describe 1eV
• Explain using diagrams what happens to
electrons passing through gases with
different speeds

3. The Electron Volt
• An electron volt is the work done (or energy
required) to move an electron through a
potential difference of 1V.
• 1 eV is the same as 1.6x10-19J
• How many Joules to move 3 electrons through
a 500V potential difference?

4. Ionisation through Collisions
• High speed electrons pass through a low
pressure gas and collide with the particles.
• They can pass on enough energy to electrons
in the shells to ionise them.
• In this collision the colliding electron will lose
energy equivalent to the ionisation energy of
the atom and the particle will become an ion.
What is an ion?

5. Excitation through collisions
• If the energy contained by the electron is not
sufficient to ionise the electron then it may be
able to at least excite it.
• The electron’s energy will be used to raise the
electron up to a higher energy level.
What do you think is likely to happen next?

6. Electron Collisions
• When electrons collide with gas particles
energy is only transferred if there is enough to
excite an electron in the gas particles shell to a
higher energy level.
• If there isn’t an elastic collision will occur and
no energy will be transferred.