Quantum physics is the study of the smallest objects in the universe: photons of electromagnetic radiation, the wavelengths of electrons and the energy levels of an atom.
Key Concepts
Photoelectric effect
The photoelectric effect provides evidence for the quantum nature of light. Individual photons of light interact with individual electrons to provide energy that may release an electron from a metal surface. Check out the page on the Photoelectric effect for a full description of the observations and explanations.
Photons have energy proportional to their frequency:
\(E=hf\)
- \(E\) is photon energy (J)
- \(h\) is Planck's constant (6.63×10−34 Js)
- \(f\) is frequency (Hz)
Conservation of energy can be applied to the photoelectric effect:
\(hf=hf_0+E_\text{max}\)
\(hf=\Phi+E_\text{max}\)
- \(f_0\) is threshold frequency for a given material (Hz)
- \(\Phi\) is work function for a given material (J)
- \(E_\text{max}\) is maximum kinetic energy
High energy interactions
Photons with more energy than is required for the photoelectric effect can transfer energy and momentum to electrons through Compton scattering. Conservation laws suggest that the photons have momentum.
The highest energy photons can convert their energy into mass, with the mass-energy equivalence calculated through \(E=mc^2\). A particle-antiparticle pair is produced to conserve charge and other properties. A particle and its antiparticle may conversely annihilate to produce a pair of photons (in opposite directions to conserve momentum).
The probability of an electron being in a particular position at a particular time is defined by Schrödinger as the square of the wave function, where the wave function varies with position and time. The wave function is denoted as \(\Psi\).
\(P(r)=|\Psi|^2\Delta V\)
- \(P(r)\) is the probability of the electron at a given radius
- \(|\Psi|\) is the magnitude of the wave equation
- \(\Delta V\) is the volume
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