43 terms

Quantum Physics


Terms in this set (...)

Blackbody Radiation
Radiation properties are independent of the material. The maximum of the distribution shifts to smaller wavelengths as the temperature is increased. The total power radiated increases with the temperature. One of the outstanding exceptions that classical physics could not explain, dubbed the "ultraviolet catastrophe" by Paul Ehrenfest.
Has the ideal property that it absorbs all the radiation falling on it and reflects none.
Discovery of the Electron
J.J. Thomson observed that monoatomic gases could be ionized by x rays/cathode rays, thus implying the atom itself must have charged constituents that can be separated. These individual parts could be deflected by an electric field as if they were negatively charged.
Crossed-Field Experiment
Performed by J.J. Thomson, attempting to determine anything about electrons. He realized he could determine their q/m ratio by finding their velocity through derivations of the equations pictured and r=(mv)/(qB).
Millikan oil-drop experiment
Robert Milikan discovered the charge and subsequent mass of the electron by balancing charged, aerosolized drops of oil with an electric field, so that mg = qE of the drop. Thus, solving for q gave him the charge of the drop. It was noted that each drop was an integer multiple of a certain minimum charge value.
Thomson's atomic model
Referred to as "plum-pudding model" or the "raisin-cake model" because of the resemblance. Thomson hypothesized the atom was a spherical cloud of positive charge with negative electrons embedded in them.
Rutherford's atomic model
Known as the "nuclear model of the atom". Rutherford hypothesized that electrons orbit a small (massive compared to electron) nucleus. This came about through his observation that some alpha particles were reflected at large angles or backwards when going through thin metal foils, believing this to be caused by the alpha particle approaching close to the nucleus and being deflected the opposite way due to their like charges.
Electron volt
1 eV = 1.60 E-19 J. Derived by determining electron kinetic energy starting from rest across a a parallel plate capacitor. In other words, 1 electron volt is the kindetic energy gained by an electron (or proton) if it accelerates through a potential difference of 1 volt.
Mass spectrometer
Device used for measuring the charge-to-mass ratio of atomic ions.
Nucleus with same Z-value, but different masses (Different # of neutrons)
Mass number
Represented by A, A = Z (protons) + N (neutrons). Not the same as atomic mass, though it is approximately the mass in atomic mass units.
Planck's radiation law
Derived by Max Planck to explain blackbody radiation.
Planck's constant
Represented by the variable h, determined from the equation E = hf. Its value is 6.6261 E-34 J*s.
Methods of electron emission
Thermionic emission (application of heat allows electrons to gain enough energy to escape), Secondary emission (electron gains enough energy by transfer from a high-speed particle that strikes the material from outside), Field emission (a strong external electric field pulls the electron out of the material), Photoelectric effect (Incident light [Electromagnetic radiation] shining on the material transfers energy to the electrons,allowing them to escape).
Ejected electrons (specifically caused by EM radiation?)
Work function
It is the minimum binding energy of the electron to the material, or inversely, it is the minimum extra kinetic energy that allows electrons to escape the material. Represented by 𝜙.
Energy quantum
E = hf
The process by which photons are emitted by an electron slowing down. ("braking radiation")
p (momentum of a particle moving at light-speed)
E/c => hf/c => h/λ
Compton effect
The process of elastic photon scattering from electrons
Pair production
The creation of an elementary particle and its anti-particle. Often refers specifically to a photon creating an electron-positron pair near a nucleus but can more generally refer to any neutral boson creating a particle-antiparticle pair.
Atomlike configuration formed from positron-electron pair. They orbit around a common center for typically 10 E-11 s.
Pair annihilation
The process of a particle and anti-particle colliding into each other to produce electromagnetic radiation.
Bohr radius
0.53 E-10 m, orbit of the hydrogen atom, represented by na_0, where n is an integer called the principal quantum number.
Absorption and Emission spectrum
The spectrum of light absorbed or emitted by an element. For example, passing white light through hydrogen gas results in particular frequencies/photons being absorbed. These same frequencies/photons are later emitted by the atom.
Fine structure constant
The ratio of the speed of a hydrogen electron in its stationary state to that of the speed of light. alpha = v_1/c = h/ma_0c = (picture)
Bohr's correspondence principle
In the limits where classical and quantum theories should agree, the quantum theory must reduce to the classical result.
De Broglie wavelength
applies to "matter waves"
Wave packet
Adding waves of different amplitudes and frequencies in particular ways results in a wave packet. Its net amplitude differs from zero only over a small region of (delta)x.
Bohr's principle of complementarity
It is not possible to describe physical observables simultaneously in terms of both particles and waves.
Uncertainty principle
Establishes limits on the simultaneous knowledge of the values of momentum and position.
Wave function
Probability density
Represented by psi squared (or its conjugate), it is the probability of finding a particle in a given volume at a given instant in time.
Integration of the probability density from negative infinity to positive infinity.
The Copenhagen interpretation
Interpretation of quantum results. Strongly supported by Max Born, Wolfgang Pauli, Bohr and Heisenberg. It promotes the collapse of the wave function upon measurement. It is generally based on the following: 1) The uncertainty principle, 2) The complementary principle, and 3) The statistical interpretation of Born, based on probability determined by the wave function.
Boundary conditions
An acceptable wave function must satisfy the Schrodinger equation and : 1) In order to avoid infinite probabilities, (PSI) must be finite everywhere, 2) In order to avoid multiple values of the probability, (PSI) bust be single values, 3) For finite potentials, (PSI) and (partial d(PSI)/dx) must be continuous, and 4) in order to normalize the wave functions, (PSI) must approach zero as x approaches + or - infinity.
Schrodinger wave equation
Time-independent Schrodinger wave equation
Expectation value
The wave function is calculated to find the expected result of the average of many measurements of a given quantity. Denoted by <x>
Physical observable
Any measurable quantity for which we can calculate the expectation value.
A mathematical operation that transforms one function into another.
Quantum tunneling
A particle is allowed by quantum mechanics and the uncertainty principle to penetrate into a classically forbidden region.
Penetration distance
Although an exponential decay does not have a sharp ending point, it can be determined "about how far" the wave function extends past the classical turning point.

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