1. How does energy change with frequency of light? Quantum Behaviour

3. But how does energy of a photon differ with frequency?

5. 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

6. 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…!

7. Measuring Energy in LEDs

8. 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 (J) (e x Voltage) Striking Voltage (V) LED Frequency (Hz) LED Wavelength LED Colour

9. Plot a graph of energy against frequency Frequency (Hz) Energy (J) Calculate the gradient – what should it equal??? Hint – think E/f = ?