Topic 3.3: Light and Atoms

Vocabulary practice flashcards covering atomic energy levels, atomic emission and absorption spectra, continuous spectra, characteristic X-rays, and the physics of lasers and stimulated emission.

Continuous Spectrum

An electromagnetic spectrum containing an unbroken range of frequencies radiated by solid, liquid, or dense gaseous objects.

Incandescence

The process by which hot solids, liquids, or dense gases emit a continuous spectrum of electromagnetic radiation whose frequency distribution and dominant colour depend directly on temperature.

Black Body Spectrum

The characteristic continuous spectrum of electromagnetic radiation emitted by hot, dense objects across various temperatures.

Line Emission Spectrum

A spectrum consisting of thin, discrete coloured lines on a dark background, produced when atoms of a pure heated gas or gas connected to a high potential difference emit specific discrete frequencies of light.

Line Absorption Spectrum

A spectrum consisting of discrete dark lines superimposed on a continuous spectrum, produced when light passes through a cooler gas and specific frequencies are absorbed by atomic electrons.

Spectral Lines

Specific discrete lines present on an emission or absorption spectrum, each representing a unique wavelength characteristic of the chemical element or compound emitting or absorbing it.

Ground State

The lowest energy state of an atom ($n = 1$), representing the state where its electrons possess the minimum possible internal energy.

Excited State

Any energy state higher than the ground state ($n > 1$) to which an electron can be promoted when the atom absorbs energy.

Collisional Excitation

The process by which an electron in an atom is raised from a lower energy state to a higher energy state by absorbing energy from a collision with an incoming particle, such as an accelerated electron.

Characteristic X-Rays

High-intensity discrete peaks in an X-ray spectrum produced when incident high-speed electrons eject inner-shell electrons from target atoms, causing outer-shell electrons to drop down and emit photons with energies equal to the transition gap.

Ionisation Energy

The minimum amount of energy required to completely remove a valence electron from an atom in its ground state ($n = 1$).

Balmer Series

The spectral series of four visible emission lines in hydrogen produced when excited electrons transition from higher energy states down to the $n = 2$ energy level.

Lyman Series

The spectral series of emission lines in hydrogen located in the ultraviolet region, produced when excited electrons drop down to the $n = 1$ ground state.

Paschen Series

The spectral series of emission lines in hydrogen located in the infrared region, produced when electrons transition from higher energy levels down to the $n = 3$ level.

Rydberg Constant ($R$)

A fundamental physical constant used in Balmer's empirical formula to calculate the wavelengths of hydrogen spectral transitions, with a value of $1.097 \times 10^7\,\text{m}^{-1}$.

Fraunhofer Lines

The dark absorption lines observed in the Sun's continuous spectrum, caused by the selective absorption of light by cooler elemental gases in the solar atmosphere.

Fluorescence

The process in which an atom absorbs a high-energy photon to enter an excited state, and then spontaneously transitions back to the ground state via intermediate steps, emitting two or more lower-energy (longer wavelength) photons.

Spontaneous Emission

The random transition of an electron from an excited state to a lower energy state without external influence, typically occurring after an average lifetime of about $10^{-8}\,\text{s}$ and emitting a photon in an arbitrary direction.

Stimulated Emission

The process where an incident photon of energy $\Delta E = h\nu$ triggers an excited electron to drop to a lower energy state, releasing a second photon identical in energy, direction, and phase to the incoming photon.

Population Inversion

A non-equilibrium condition required for laser operation in which a greater number of atoms occupy a higher energy (metastable) state than a lower energy state.

Metastable State

An excited atomic state with an unusually long lifetime (approximately $10^{-3}\,\text{s}$ compared to the standard $10^{-8}\,\text{s}$), allowing sufficient accumulation of excited atoms to establish a population inversion.

Laser (Light Amplification by Stimulated Emission of Radiation)

A device that generates a narrow, intense, monochromatic, and coherent beam of light via stimulated emission within an optical resonant cavity.

Gain Medium

The active substance in a laser containing atoms or molecules that undergo stimulated emission to amplify light.

Pump (Laser)

The external energy source (such as an electrical potential difference) that provides the energy required to excite atoms in the gain medium and maintain a population inversion.

Coherence

A property of laser light in which all emitted photons maintain a constant phase relationship relative to one another over large distances, enabling the beam to remain highly focused and uni-directional.