Physics | 13 Quantum And Nuclear

Front 1

Photoelectric effect

Back 1

The ejection of surface electrons, typically from a metal surface, upon the incidence of electromagnetic waves with a high-enough energy-per-photon content.

FD: Ultimately it is the value of the energy-per-photon, and not the number of photons, that determines whether photoelectrons are ejected

Front 2

Photoelectrons

Back 2

Electrons that are emitted as a result of the photoelectric effect

Front 3

Work function

Back 3

FD: The minimum photon energy required to cause the ejection of a photoelectron with no residual kinetic energy

Front 4

Threshold frequency

Back 4

FD: The frequency of the incident EM wave that has a photon energy whose value equals to the work function of the surface of the metal

Front 5

Stopping voltage

Back 5

FD: A voltage that will just prevent from photoelectrons that are emitted off a surface from arriving at the opposite terminal

Front 6

EM wave intensity

Back 6

FD: For IB purposes, intensity = power/area = energy/time/second = energy per photon x number of photons/time/area

Front 7

De Broglie wavelength

Back 7

The wavelength of particles is inversely proportional to their momentum: λ = h/p = h/mv

Front 8

Wave-particle duality

Back 8

A hypothesis that everything exhibits both particle-like and wave-like behaviour. The higher the mass, the less significant the wave-like behaviour.

Front 9

Davisson-Germer experiment

Back 9

An experiment that demonstrated that electrons undergo diffraction upon passing through e.g. a lattice of metal atoms within a crystal. This supports the wave-like behaviour of electrons

Front 10

Atomic spectra

Back 10

Emission or absorption spectra that features increased or decreased intensity at particular wavelengths within a wider range of wavelengths, due to electrons undergoing transitions, absorbing or releasing photon energy in the process

Front 11

Transitions

Back 11

FD: A process that involves excitation (e.g. electrons absorbing EM radiation or other forms of energy as they go to higher energy levels) or relaxation (electrons releasing EM radiation, or other forms of energy as they cascade down energy levels)

Front 12

Energy quantization

Back 12

The energy levels for electrons within an atom are discrete. Only specific values of energies are allowed.

FD: This explains the discrete nature of a line spectrum arising from electronic transitions

Front 13

Electron-in-a-box model

Back 13

A model that assumes that if an electron is confined to move in one dimension within a box, then the de Broglie waves associated with the electrons will be standing waves that satisfy the boundary condition of the box i.e. nodes at each end. The lowest energy state will feature the longest possible wavelength, which is twice the length of the box.

FD: The kinetic energy of the electron = n2h2/8m2L2. This equation will be given.

Front 14

Schrodinger model

Back 14

An atomic model that assumes that electrons in the atom may be described by wavefunctions. The electron has an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electrons within a particular region of space.

Front 15

Wavefunction

Back 15

A mathematical expression that has no particular physical meaning, but when squared and integrated, the probability of finding electrons within a particular range of distance + angles away from the nucleus can be obtained

Front 16

Heisenberg uncertainty principle

Back 16

Conjugate quantities of a particle cannot be both known precisely at the same time

FD: The conjugate quantities of interest as per the IB syllabus include position-momentum and time-energy

Front 17

Bainbridge mass spectrometer

Back 17

An instrument that allows atoms of different masses and/or charges to reach a detector by the careful adjustment of accelerating voltages and deflecting magnetic field strengths.

FD: A mass spectrometer provides evidences for the existence of isotopes of elements

Front 18

Nuclear energy levels

Back 18

FD: Atomic nuclei have discrete energy levels. Evidence for this would be the discrete kinetic alpha-particle energy and discrete gamma-photon energy that are both released during an alpha decay

Front 19

ß+ decay

Back 19

A decay that features a proton being converted into a neutron, a positron, and an electron neutrino

FD: Students must be aware that the beta-particles (ß+ and ß-) have a range of energies as opposed to discrete energies. A 3-particle "fission" involving neutrinos travelling in random directions is postulated to explain the many possible energy content of beta particles

Front 20

Decay constant

Back 20

The probability of decay per unit time (e.g. second) for a particular radioisotope.