Quantum Physics

Black Body Radiation Intensity of blackbody radiation Classical Rayleigh-Jeans law for radiation emission Planck’s expression h =  J · s : Planck’s constant Assumptions: 1. Molecules can have only discrete values of energy E n; 2. The molecules emit or absorb energy by discrete packets - photons

Quantum energy levels Energy E n hf 2hf 3hf 4hf 0 5hf

Photoelectric effect Kinetic energy of liberated electrons is where  is the work function of the metal

Atomic Spectra a)Emission line spectra for hydrogen, mercury, and neon; b)Absorption spectrum for hydrogen.

Bohr’s quantum model of atom +e e r F v 1. Electron moves in circular orbits. 2. Only certain electron orbits are stable. 3. Radiation is emitted by atom when electron jumps from a more energetic orbit to a low energy orbit. 4. The size of the allowed electron orbits is determined by quantization of electron angular momentum

Bohr’s quantum model of atom +e e r F v Newton’s second law Kinetic energy of the electron Total energy of the electron Radius of allowed orbits Bohr’s radius (n=1) Quantization of the energy levels

Bohr’s quantum model of atom Orbits of electron in Bohr’s model of hydrogen atom. An energy level diagram for hydrogen atom Frequency of the emitted photon Dependence of the wave length

The waves properties of particles Louis de Broglie postulate: because photons have both wave and particle characteristics, perhaps all forms of matter have both properties Momentum of the photon De Broglie wavelength of a particle

Example: An accelerated charged particle An electron accelerates through the potential difference 50 V. Calculate its de Broglie wavelength. Solution: Energy conservation Momentum of electron Wavelength