Glossary
Energy Levels
Discrete, quantized values of energy that electrons can possess within an atom, rather than a continuous range of energies.
Example:
When an electron in a neon sign jumps between specific energy levels, it emits photons of a characteristic red color.
Half-Life
The characteristic time it takes for half of the radioactive nuclei in a given sample to undergo radioactive decay.
Example:
If a medical isotope has a half-life of 6 hours, then after 12 hours, only one-quarter of the original sample will remain.
Probability Density
The square of the absolute value of the wave function (|Ψ|²), which represents the likelihood of finding a particle at a specific location in space.
Example:
A high peak in a probability density plot for an electron in a quantum well indicates a region where the electron is most likely to be found.
Radioactive Decay
A spontaneous, probabilistic process where an unstable atomic nucleus transforms into a more stable one by emitting particles and energy.
Example:
Carbon-14 undergoes radioactive decay to nitrogen-14, a process used in archaeological dating to determine the age of ancient artifacts.
Spectral Lines
Distinct lines of light observed in emission or absorption spectra, corresponding to the specific photon energies emitted or absorbed during electron transitions between atomic energy levels.
Example:
Astronomers can identify the chemical composition of distant stars by analyzing the unique pattern of spectral lines in their emitted light.
Spontaneous Emission
The process where an electron in an excited atomic state randomly drops to a lower energy level, emitting a photon without any external trigger.
Example:
The glow from a firefly is due to spontaneous emission of light from excited molecules within its body.
Standing Waves
Wave patterns that remain in a constant position, formed by the superposition of two waves traveling in opposite directions, used to model electron states in atoms.
Example:
Just like a vibrating guitar string forms standing waves with fixed nodes, electrons in an atom exist in specific orbital patterns that resemble these waves.
Stimulated Absorption
The process where an atom in a lower energy state absorbs an incoming photon with precisely the right energy, causing an electron to jump to a higher, excited energy level.
Example:
For a solar cell to work efficiently, its material must exhibit strong stimulated absorption of photons from sunlight.
Stimulated Emission
The process where an incoming photon causes an excited atom to emit an identical photon as it transitions to a lower energy state, forming the basis for laser operation.
Example:
Lasers achieve their intense, coherent light by harnessing stimulated emission, where one photon triggers a cascade of identical photons.
Wave Function (Ψ)
A mathematical description of a quantum particle's state, varying in space and time, which contains all possible information about the particle.
Example:
In a hydrogen atom, the wave function for an electron describes its probability distribution around the nucleus, rather than a fixed orbit.
Wave-Particle Duality
The fundamental concept in quantum mechanics that particles can exhibit both wave-like and particle-like properties, depending on how they are observed.
Example:
The famous double-slit experiment beautifully illustrates wave-particle duality, showing electrons behaving as waves when unobserved and as particles when detected.
de Broglie Wavelength (λ = h/p)
The wavelength associated with a particle, inversely proportional to its momentum (p), demonstrating the wave-like nature of matter.
Example:
A fast-moving electron in an electron microscope has a very short de Broglie wavelength, allowing it to resolve incredibly small structures.