Quantum physics

Quantum physics

1. Photoelectric effect

   • The photoelectric effect is when photons hit a metal passing its energy directly to the delocalised electrons removing them from the surface of the metal
   • Threshold frequency
     • Only a higher enough frequency carry enough energy to over come the work function of a metal, this is known as the threshold frequency
   • Proving the photoelectric effect
     • You can use a gold leaf electroscope to prove the photoelectric effect, when a negative charge is put through the apparatus the gold leaf is repelled from the metal bar as it has the same charge(-). To get rid of this negative charge UV light is shone onto the metal cap this removes the excess electrons. By removing the negative charge the gold leaf is no longer repelled so returns to the side of the bar
   • Einsteins photoelectric equation
     • E = hf = Ek + Φ
       • where Φ is the work function F is frequency h is planks constant and Ek is kinetic energy
       • Work function is the minimum energy required to release an electron from a metal

2. Energy of a photon

   • A photon is a quantum packet of energy and is measured in electron volts
     • 1Ev=1.6*10-19 J
   • Energy of a photon = planks constant *frequency e=hf
   • Planks constant is equal to 6.63*10-34 J/S

3. Wave particle duality

   • De broglie discovered that light behaves as a wave and as a particle
   • Wavelength = Plancks constant/momentum λ = h/mv

4. Speed of light

   • v = fλ Use this equation for electrons not photons
   • c = fλ Use this for electromagnetic waves where c is the speed of light
   • E = hc/λ Use this to find the energy of a photon

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