Fundamental particles (2) Flashcards
Electromagnetic spectrum
in order of decreasing wavelength, the members are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Quantum of energy
a small packet of energy. The word quantum means discrete or separate.
Photon
the name given to a discrete packet (quantum) of electromagnetic energy.
Inverse square law
applies when a quantity, such as intensity, is inversely proportional to the square of the distance from the source.
Electron volt, eV
a unit of energy equal to 1.6 x 10-19J. It is the energy gained by an electron when it is accelerated through a potential difference of 1 volt.
Energy levels
electrons can only occupy a small number of separate energy levels within an atom. Electrons in an atom move between different energy states or levels when they absorb or emit a photon.
Ground state
when electrons in an atom are in their lowest energy state, they are in the ground state.
Excitation
when an electron in an atom moves to a higher energy level (above the ground state) after it has absorbed energy, it is in an excited state. Excitation has occurred.
Ionisation
occurs when an atom gains or loses an electron and becomes charged. It has been ionised.
Ionisation energy
is the energy required to remove an electron from its ground state to infinity, i.e. to become detached from the atom.
Diffraction grating
a piece of transparent material ruled with very closely spaced lines, used to see the diffraction of light.
Continuous spectrum
a spectrum where all frequencies of radiation or colours of light are possible.
Line spectrum
a spectrum of discrete coloured lines of light.
Emission spectrum
a bright spectrum seen when photons are emitted by atoms.
Absorption spectrum
a spectrum of dark lines seen on a coloured background produced when a gas absorbs photons.
