Topic 13: Nuclear and Quantum Physics Flashcards
Photoelectric effect
When light shines on a clean metal surface, electrons are emitted from the surface.
Threshold frequency
Below this frequency of incident light, no photo-electrons are emitted.
Stopping potential
The opposing PD necessary to stop the photo-electron current. A measure of the maximum KE of electrons.
Work function
Minimum energy required for electrons to escape from a particular metal surface.
Photon
Packet of light energy. Energy is proportional to frequency of light.
Einstein explanation for photoelectric effect
Light energy is quantised and energy of a photon is fixed by its frequency. Electron can absorb photon and leave the energy surface with KE = photon energy – work function.
De Broglie Hypothesis
All moving particles have wave properties and in particular a wavelength calculated from the de Broglie equation. These properties are generally only significant for the very small or very fast.
Davisson Gerlach experiment
Electrons incident on a crystal are diffracted if atomic spacing is similar to de Broglie wavelength.
Emission spectra
An element which is given enough energy emits light at particular frequencies which form a characteristic line spectrum which can be used to identify the element.
Absorption spectra
White light shone through a hot gas will have dark lines in its continuous spectrum due to absorption at its characteristic frequencies.
Evidence for quantisation
Electrons in an atom exist only at fixed energy levels. Any transition from one level to another involves a fixed amount of energy which is emitted or absorbed as a quantum with an associated frequency.
Electron in a box
A simplified version of electrons in the atom considers them as standing waves in one dimension.
Shroedinger’s model
Electrons can be considered as wavefunctions. For the wavefunction, (amplitude)2 is proportional to probability of finding an electron at a given point.
Heisenberg’s uncertainty principle
It is impossible to measure exactly the momentum and position of a particle simultaneously. This is also true of energy and time.
Beta decay
The emission from the nucleus of an electron or a positron (antiparticle of electron). The energies of the emitted particles form a continuous spectrum.
