particles

what is an electron volt

• The energy gained by an electron travelling through a potential difference of one volt

• to convert eV -> J: multiply by 1.6 × 10^-19 (EJX)

what is the photoelectric effect

• When electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation

• It is evidence of light being a particle

what is the threshold frequency

• The minimum frequency (at maximum wavelength) of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal

what is the work function

• The minimum energy required to release a photoelectron from the surface of a metal

• KEmax = hf - work function

why is kinetic energy a maximum in the equation KEmax = hf - work function

• electrons are at different depths in the metal

• An electron emitted from the surface will have KE max

• an electron emitted from deeper will require more energy to be emitted, meaning less if leftover as kinetic energy

what is excitation

• When an electron absorbs enough energy to move up to a higher energy level

• This requires the electron to absorb a photon with the same energy as a difference in energy levels in the atom

• Or it can absorb an electron

how do fluorescent tubes work

• Beam electrons collide with the electrons in the mercury atoms, causing them to gain energy and excite

• The electrons then deexcite, emitting photons in the UV range of wavelengths

• These UV photos then collide with the electrons in the atoms of the phosphor coating, and excite them

• The phosphor electrons deexcite in stages, emitting photons in the visible light range of wavelengths

evidence for light as a particle

• the photoelectric effect

evidence for light as a wave

• diffraction and interference of light in Young’s double slit experiment

• de Broglie’s electron diffraction

electron diffraction

• a diffraction pattern is produced when a beam of electrons is directed at a thin graphite film

• for this to be observed, the electrons must be focused through a gap similar in size to their de Broglie wavelength

• the diffraction pattern is a series of concentric rings

factors effecting the radius of the electron diffraction pattern

• the longer the wavelength, the larger the radius of the rings

• the larger the accelerating voltage, the smaller the radius of the rings

what is specific charge

• the ratio of the total charge of a particle to its mass

• specific charge = Q/m

what is an isotope

nuclei that have the same number of protons but different numbers of neutrons

why is a neutrino emitted in beta minus decay

• number of beta particles plotted against kinetic energy gives a curve

• this shows that beta particles have a continuous range of energies

• the energy released in beta decay must therefore be shared between the beta particle and the neutrinos in order to conserve energy