Glossary
Binding Energy (Work Function)
The minimum amount of energy required to remove an electron from the surface of a particular metal in the photoelectric effect.
Example:
For an electron to be ejected from a metal, the incoming photon must have energy greater than the metal's binding energy, also known as its work function.
Blackbody
An idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence, and emits thermal radiation perfectly.
Example:
A theoretical blackbody would absorb all light hitting it, appearing perfectly black, and then emit radiation based solely on its temperature, like a glowing hot piece of metal.
Dalton Model
An early atomic model proposing that atoms are indivisible, indestructible spheres of a given element, and that atoms of different elements have different masses.
Example:
John Dalton's model helped explain why elements combine in fixed ratios, like how hydrogen and oxygen always form water in a specific proportion, treating each atom as a distinct, indivisible sphere.
Electron Orbitals
Regions around the nucleus where there is a high probability of finding an electron, described by quantum mechanics rather than fixed paths.
Example:
Instead of electrons orbiting like planets, quantum mechanics describes their probable locations within specific three-dimensional shapes called electron orbitals.
Energy (E)
The capacity to do work or produce heat, in the context of light, it refers to the energy carried by photons.
Example:
Ultraviolet light carries more energy per photon than visible light, which is why it can cause sunburn.
Frequency (ν)
The number of wave cycles that pass a fixed point per unit of time, typically measured in Hertz (Hz) or s^-1.
Example:
A high-pitched sound has a high frequency, meaning more sound waves pass your ear per second.
Kinetic Energy (KE)
The energy an object possesses due to its motion, specifically referring to the energy of ejected electrons in the photoelectric effect.
Example:
In the photoelectric effect, if a photon has more energy than the binding energy, the excess energy is converted into the kinetic energy of the ejected electron.
Nucleus
The dense, positively charged center of an atom, containing protons and neutrons, which was discovered by Rutherford's experiment.
Example:
The atom's mass is primarily concentrated in its tiny nucleus, which is why alpha particles were occasionally repelled directly backward during the gold foil experiment.
Photoelectric Effect
The phenomenon where electrons are ejected from a metal surface when light of a sufficiently high frequency shines on it, demonstrating the particle nature of light.
Example:
Solar panels work because of the photoelectric effect, where photons from sunlight strike a material and knock electrons loose, generating an electric current.
Photons
Discrete packets or quanta of light energy, proposed by Einstein to explain the photoelectric effect, demonstrating that light behaves as both a wave and a particle.
Example:
When you see light, you are observing streams of tiny energy packets called photons interacting with your eyes.
Planck's Constant (h)
A fundamental physical constant that relates the energy of a photon to its frequency, with a value of approximately 6.626 x 10^-34 Js.
Example:
To calculate the energy of a single photon, you multiply its frequency by Planck's constant, a tiny but crucial number in quantum mechanics.
Planck's Equation (E = hν)
An equation stating that the energy (E) of a photon is directly proportional to its frequency (ν), with Planck's constant (h) as the proportionality constant.
Example:
Using Planck's equation, we can determine that a photon of blue light, with its higher frequency, carries more energy than a photon of red light.
Quanta
Discrete packets or bundles of energy, as proposed by Max Planck, meaning energy is not continuous but comes in specific, quantized amounts.
Example:
Planck revolutionized physics by suggesting that light energy is not continuous but comes in tiny, indivisible packets called quanta.
Rutherford's Gold Foil Experiment
A landmark experiment where alpha particles were shot at a thin gold foil, leading to the discovery that atoms are mostly empty space with a tiny, dense, positively charged nucleus.
Example:
The surprising deflection of some alpha particles in Rutherford's gold foil experiment indicated that the atom's positive charge and most of its mass were concentrated in a very small central region.
Speed of Light Equation (c = λν)
An equation relating the speed of light (c) to its wavelength (λ) and frequency (ν), showing that wavelength and frequency are inversely proportional.
Example:
Using the speed of light equation, we can calculate that radio waves, with their very long wavelengths, must have very low frequencies.
Thomson's Plum Pudding Model
An atomic model suggesting that an atom is a sphere of uniformly distributed positive charge with negatively charged electrons embedded within it, like raisins in a pudding.
Example:
Before Rutherford, scientists imagined the atom as a diffuse positive cloud with electrons scattered throughout, much like the plum pudding model where the 'plums' are electrons in a positive 'pudding'.
Threshold Frequency
The minimum frequency of light required to cause the photoelectric effect, below which no electrons will be ejected, regardless of light intensity.
Example:
Even very bright red light won't cause the photoelectric effect in some metals because its frequency is below the threshold frequency required to eject electrons.
Ultraviolet Catastrophe
A major discrepancy between classical physics predictions and experimental observations of blackbody radiation, where classical theory predicted infinite energy emission at high frequencies.
Example:
Classical physics failed to explain why hot objects don't emit infinite amounts of high-frequency light, a problem famously known as the ultraviolet catastrophe.
Wave-Particle Duality
The concept that light and matter exhibit properties of both waves and particles, depending on the experimental conditions.
Example:
The wave-particle duality of light means it can diffract around obstacles like a wave, but also knock electrons off a surface like a particle.
Wavelength (λ)
The distance between successive crests or troughs of a wave, typically measured in meters or nanometers.
Example:
Visible light ranges from violet, with a short wavelength, to red, with a long wavelength.