Glossary
Classical Mechanics Limitations
The inability of classical physics to accurately describe phenomena at very small scales (atomic and subatomic) or very high speeds.
Example:
Understanding the stability of an atom's electron orbits requires quantum mechanics, as classical mechanics limitations would predict electrons spiraling into the nucleus.
De Broglie Wavelength (λ=h/p)
The wavelength associated with a moving particle, inversely proportional to its momentum, demonstrating the wave-like nature of matter.
Example:
An electron accelerated in a cathode ray tube has a measurable de Broglie wavelength, allowing it to exhibit diffraction.
Discrete Energy Levels
Specific, fixed amounts of energy that a bound system, like an electron in an atom, can possess, rather than any continuous value.
Example:
When an atom emits light, it's because an electron transitioned between two discrete energy levels, releasing a photon with a specific energy.
Energy of a Photon (E=hf)
The energy carried by a single photon, which is directly proportional to its frequency, where 'h' is Planck's constant and 'f' is the frequency.
Example:
A blue light photon has a higher energy than a red light photon because blue light has a higher frequency.
Excited States
Higher energy levels that an electron or other quantum system can occupy when it absorbs energy, typically unstable.
Example:
When a neon sign glows, electrons in the neon gas are jumping to excited states and then falling back, emitting light.
Frequency (f)
For a wave, the number of complete cycles or oscillations that occur per unit of time, typically measured in Hertz (Hz).
Example:
A radio station broadcasts at a specific frequency, which determines the energy of the photons carrying the signal.
Ground State
The lowest possible energy level that an electron or other quantum system can occupy.
Example:
An electron in a hydrogen atom typically resides in its ground state unless energy is added to excite it.
Momentum (p)
A measure of the mass and velocity of an object, calculated as the product of mass and velocity (p=mv).
Example:
A bowling ball rolling down an alley has significant momentum, making it hard to stop.
Particle in a Box
A simplified quantum mechanical model that describes a particle confined to a small, one-dimensional region, illustrating the quantization of energy.
Example:
The particle in a box model helps us understand why electrons in a quantum dot have quantized energy levels.
Photon
A discrete packet or quantum of light or other electromagnetic radiation, carrying a specific amount of energy.
Example:
When you see a flash of light, you are observing billions of individual photons interacting with your eyes.
Planck's Constant (h)
A fundamental physical constant that relates the energy of a photon to its frequency, central to quantum mechanics.
Example:
To calculate the energy of a specific photon, you'll always need to use Planck's constant in the E=hf equation.
Quantization
The concept that certain physical quantities, such as energy or angular momentum, can only take on discrete, specific values rather than a continuous range.
Example:
The fact that electrons in an atom can only exist at specific energy levels is a direct consequence of quantization.
Quantum Theory
A fundamental theory in physics that describes the behavior of matter and energy at the atomic and subatomic levels, explaining phenomena classical mechanics cannot.
Example:
Quantum theory successfully explains why atoms emit light at specific colors, leading to unique atomic spectra.
Speed of Light (c)
The speed at which all electromagnetic radiation, including light, travels in a vacuum, approximately 3.00 x 10^8 m/s.
Example:
Even though light from the sun takes about 8 minutes to reach Earth, it travels at the incredible speed of light.
Wave-Particle Duality
The concept that all particles exhibit both wave-like and particle-like properties, and all waves exhibit both wave-like and particle-like properties.
Example:
Light demonstrates wave-particle duality when it diffracts like a wave but also knocks electrons off a surface like a particle (photon).
Wavelength (λ)
The spatial period of a periodic wave, the distance over which the wave's shape repeats, typically measured in meters.
Example:
Infrared light has a longer wavelength than visible light, which is why we can't see it directly.