Many Paths
0 likes250 views
1) Light can be represented as both a wave and particle. Photons carry light energy, with higher frequency photons having more energy. 2) Energy of a photon is calculated using Planck's constant and frequency, with E=hf. For small energies, electron volts (eV) provide a more useful unit than joules. 3) Measuring the striking voltage of LEDs of different colors allows calculating the corresponding photon energies in eV. A graph of energy versus frequency can then be made.
1 of 9
More Related Content
What's hot (19)
Viewers also liked (20)
Ad
Similar to Many Paths (20)
Ad
More from PhysicsJackson (20)
Recently uploaded (20)
PDF
Buy Verified Payoneer Account – 100% Best With All Documents.pdfbuypaypalaccountsee buypaypalaccountsBuy Verified Payoneer Account – 100% Best With All Documents.pdfbuypaypalaccountsee buypaypalaccounts
Many Paths
- 1. How can light be represented by phasors? Quantum Behaviour
- 2. Write down something that shows light behaving as: A wave A particle (quanta)
- 3. But how does energy of a photon differ with frequency?
- 4. 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
- 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 (eV) (e x Voltage) Striking Voltage (V) LED Frequency (Hz) LED Wavelength LED Colour
- 9. Plot a graph of energy against frequency Frequency (Hz) Energy (eV) Calculate the gradient – what should it equal??? Hint – think E/f = ?