How can light be represented by phasors? Quantum Behaviour
Write down something that shows light behaving as:
A particle (quanta)
But how does energy of a photon differ with frequency?
Photons and Energy
A photon carries light energy
A red photon has less energy than a violet photon
Red Violet You could think of them like this – in terms of energy Energy = Planck’s Constant x frequency E = hf h = 6.6 x 10 -34 Js
Measuring Energy – Joules and eV We measure energy in Joules However, when this is very small, Joules are not the most useful unit to use. We use another unit – the electron Volt – eV Energy in eV = Energy in Joules / Charge on electron (e) eV = Joules/Coulombs Note ‘e’ = 1.6 x 10 -19 C
Measuring Energy – Joules and eV e.g. what is the energy in eV of 1 x 10 – 19 J? Energy in eV = Energy in Joules / Charge on electron (e) eV = 1 x 10 -19 / 1.6 x 10 -19 = 0.63 eV This is much more manageable…!
Measuring Energy in LEDs
Results e = 1.6 x 10 -19 C is Voltage needed to just light LED Striking Voltage c = 300 000 000 Frequency = c / Notes Energy (eV) (e x Voltage) Striking Voltage (V) LED Frequency (Hz) LED Wavelength LED Colour
Plot a graph of energy against frequency Frequency (Hz) Energy (eV) Calculate the gradient – what should it equal??? Hint – think E/f = ?