1. Quantum Physics – Photons Mr Nesbo

2. Learning Objectives To know what a photon is.
To know how to calculate the energy of a photon.
To be able to calculate how many photons are emitted by a light source every second.

3. Electromagnetic Spectrum
Part of E-M Spectrum
Wavelength Range
Visible nm

4. Electromagnetic Spectrum
Part of E-M Spectrum
Wavelength Range
Radio
> 0.1m
Microwave
0.1m to 1mm
Infrared
1 mm to 700 nm
Visible nm
Ultraviolet
400 nm – 1 nm
X-rays
< 1 nm
Gamma-rays

5. Mnemonic? Rabbits  Radio Mate  Microwaves In  Infrared
Very  Visible
Unusual  Ultraviolet
X-rated  X-rays
Gardens  Gamma Rays
Highest energy? Highest frequency?

6. Video
In Search of Giants (11 of 15) The Weird Quantum World.wmv

7. Wave Equation (GCSE) Recall from GCSE:-
Electromagnetic radiation travels at the speed of light which is 3.00 × 108 m s-1 in a vacuum.

8. Wave Equation (AS Physics)
In AS we write this equation using symbols:-
where c = the speed of light in a vacuum (m s-1)
f = the frequency of e-m radiation (Hz)
λ = the wavelength of e-m radiation (m)

9. Photon Energy
We can work out the energy of an incoming photon using this equation:-
Where E = Energy of Photon in Joules (J)
f = Frequency of the Radiation in Hertz (Hz)
h = Planck’s constant = 6.63 x Js
Or in words:-

10. Photon Energy
Recall from GCSE that f = c/λ so we can substitute this into the photon energy equation E=hf to get:
Or in words:-

11. Worked Example
Q: What is the photon energy for UV radiation with a wavelength 400 nm?
λ = 400 nm = 400 × 10-9 m
E = ?
h = 6.63 × J s
c = 3 × 108 ms-1