Topic 3: Quantum Phenomena Flashcards
Threshold Frequency
Minimum frequency of light that can cause photoelectric emission
Wavelength
The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time
e.g., distance between two adjacent wave peaks
Work function (of a metal)
Minimum amount of energy needed by an electron to escape from a metal surface
Photoelectric effect
Emission of electrons from a metal surface when the surface is illuminated by light of frequency greater than a minimum value known as the threshold frequency
Intensity of radiation
At a surface is the radiation energy per second per unit area at normal incidence to the surface
The unit of intensity is
Ion
A charged atom
Ionisation
Process of creating ions
Ionising radiation
Radiation that produces ions in the substances it passes through. It destroys cell membranes and damages vital molecules such as DNA directly or indirectly by creating ‘free radical’ ions which react with vital molecules
Electron volt
Amount of energy equal to 1.6 x 10^-19 J, defined as the work done when an electron is moved through a pd of 1V
Excitation
Process in which an atom absorbs energy without becoming ionised as a result of an electron inside an atom moving from an inner shell to an outer shell
Ground state
The lowest energy state of an atom
Excited state
An atom which is not in its ground state
Energy levels
The energy of an electron in an electron shell of an atom or the allowed energies of a nucleus
De-excitation
Process in which an atom loses energy by photo emission, as a result of an electron inside an atom moving from an outer shell to an inner shell or in which an excited nucleus emits a gamma photon
Flourescence
Glow of light from a substance exposed to ultraviolet radiation; the atoms de-excite in stages and emit visible photons in the process
Diffraction
The spreading of waves when they pass through a gap or round an obstacle
X-ray diffraction is used to determine the structure of crystals, metals and long molecules
Electron diffraction is used to probe the structure of materials
High-energy electron scattering is used to determine the diameter of the nucleus
de Broglie hypothesis
The idea that matter particles also have a wave-like nature
de Broglie wavelength
A particle of matter has a wave-like nature which means that it can behave as a wave. For example, electrons directed at a thin crystal are diffracted by the crystal. The de Broglie wavelength of a matter particle depends on its momentum in accordance with de Broglie’s equation wavelength = h/p = h/mv where h is the Planck constant
