Chapter 28 - Quantum Physics

diffraction

the spreading of a wave when it passes through a gap or past the edge of an object

interference

the formation of points of cancellation and reinforcement where two coherent waves pass through each other or the superposition of two or more waves from coherent sources

photoelectric effect

an interaction between a photon and an electron in a metal in which the electron is removed from the surface of a metal

photons

a quantum of electromagnetic radiation (energy)

Planck constant

a fundamental constant that links the energy of a photon E and its frequency f; E=hf (where E is photon energy, h is Planck constant, and f is frequency)

electronvolt (eV)

the energy gained by an electron travelling thorugh a potential difference of 1 volt. 1 eV= 1.60 × 10^-19 J

eV to J: multiply by 1.60 × 10^-19

J to eV: divide by 1.60 × 10^-19

threshold voltage

the minimum forward bias potential difference across a light-emitting diode (LED) when it starts to conduct and emit light

threshold frequency

the minimum frequency of the incident electromagnetic radiation that would eject electrons from the surface of a metal

threshold wavelength

the longest wavelength of the incident electromagnetic radiation that would eject electrons from the surface of a metal

work function energy

the minimum energy needed by an electron to free itself from the surface of a metal. Work function (together with threshold frequency and threshold wavelength) is a property of the metal

dispersion

the splitting of light into its component wavelengths; this can be done using a prism or a diffraction grating

continuous spectrum

an emission spectrum that consists of a continuum of wavelengths

emission line spectra

a spectrum with bright coloured lines of a unique wavelengths (composition of light emitted by hot gases)

absorption line spectra

a spectrum with dark lines of a unique wavelengths seen against the background of a continuous spectrum (composition of light emitted by cool gases)

energy levels (energy states)

a quantised energy state of an electron in an atom

quantised

a quantity is said to be quantised when it has a definite minimum magnitude and always comes in multiples of that magnitude. Restricting a variable, observable quantity to discrete values

transition

term used to describe a jump made by an electron between two energy levels

ground state

the lowest energy state that can be occupied by an electron in an atom

de Broglie wavelength

the wavelength associated with a moving particle