AQA Quantum Physics and Electromagnetic Radiation

Photon Energy

• Energy of a photon: ( E = hf )
  • ( h ) (Planck's constant) = ( 6.63 \times 10^{-34} ) Js
  • ( f ) (frequency)
• Substituting frequency ( f = \frac{c}{\lambda} ) gives ( E = \frac{hc}{\lambda} )
  • These are key equations: ( E = hf ) and ( E = \frac{hc}{\lambda} )

Photoelectric Effect

• Definition: Occurs when a photon releases an electron from a metal surface.
• Threshold Frequency ( f_0 ): Minimum photon frequency needed to release an electron.
• Work Function ( \Phi ): Minimum energy required to release an electron, ( \Phi = hf_0 ).
• Experiment: Proves particle nature of light (contradicts wave theory prediction).
• Example: Gold leaf electroscope shows electron emission with UV light.
• Equation: ( hf = \Phi + KE_{max} )_

Calculations and Examples

• Converting energy from eV to Joules: ( 1 , \text{eV} = 1.6 \times 10^{-19} , \text{J} )
• Example problem: Given work function and photon frequency, calculate kinetic energy and stopping potential.

Photoelectric Effect Equation

• Form: ( hf = \Phi + KE_{max} ) or ( \frac{hc}{\lambda} = \Phi + KE_{max} )
• Graphical Analysis: Plotting ( KE_{max} ) vs. frequency:
  • Slope ( = h )
  • X-intercept ( = f_0 )
  • Y-intercept ( = -\Phi )_

Collisions of Electrons with Atoms

• Ionization and Excitation: Electrons collide with atoms, exciting them, leading to photon emission in Mercury tubes.
• Emission: UV photons absorbed, visible photons emitted after de-excitation.

Energy Levels and Photon Emission

• Line Spectra: Evidence of discrete energy levels.
• Photon Emission: Electrons absorb/emit photons equal to energy level differences.
• Wave-Particle Duality: Light behaves as particles in photoelectric effect; electrons show wave behavior in diffraction.

De Broglie Wavelength

• Equation: ( \lambda = \frac{h}{mv} )
• Applications: Explains electron diffraction patterns.
• Impact of kinetic energy changes on ( \lambda ).

Practical Applications

• Photo Cells: Demonstrate photoelectric effect with a circuit.
• Stopping Potential: Voltage required to stop electron emission.

Summary

• Quantum physics demonstrates dual nature of light and matter.
• Energy levels, photon interactions, and wave-particle duality are core concepts.

Next Steps

• Further studies on electromagnetic waves and deeper exploration into related physics topics.