13 - Quantum Physics Flashcards
define electronvolt
energy acquired by an electron when it passes through a potential difference of 1V
photoelectric effect prediction by wave theory
the emission occurs almost instantly whereas wave theory predicts that the emission would take time
define work function
(φ) the minimum amount of energy required to release an electron from the surface of a metal
E=hf
so φ=hf0
photoelectric effect
when a photon of sufficient energy releases a photoelectron from a metal surface
define threshold frequency
(f0) minimum photon frequency required to release a photon from the surface of a metal
release of photoelectron in relation to energy of phtoton
if energy of photon > work function, electron emitted
if energy of photon < work function, not emitted
the photoelectric effect is a _______ between photons and electrons
one-to-one interaction meaning
photoelectric effect demonstrated by gold-leaf electroscope
a zinc plate on top of a negatively charged stem, with a negatively charged piece of gold leaf attached to the stem (charged using plastic rod or -ve electrode)
gold leaf and stem have same charge so repel
if visible light is shone onto the zinc plate, no electrons are emitted as the energy of photon < work function
UV light shining on the zinc plate results in electron being emitted from the surface of the metal as energy of photon > work function
electrons are emitted so negative charge is lost resulting in gold leaf falling back to stem
conclusions of photoelectric effect
maximum kinetic energy of photoelectrons increases with the frequency of the radiation
maximum kinetic energy of photoelectrons is independent of intensity of incident radiation
rate of photoelectron emission is directly proportional to intensity of incident radiation
(one to one interaction and supports PARTICLE behaviour)
KEmax
remaining energy of incident radiation transferred to kinetic energy of photoelectron due to conservation of energy
hf =φ + KEmax
different metals have different
work functions
why is it KEmax
some electrons are closer to the positive metal ions and need more energy to free them. electrons that only require minimum amount of energy to be freed (surface) will have most energy left over from incident photon and will travel faster
evidence for wave-particle duality
photoelectric effect - particle behaviour
electrons are particles (mass and charge)
can be accelerated and deflected by mag .and elec. fields but they can diffract and form diffraction patterns - wave behaviour
electron diffraction
electron gun fires electrons at thin slice of polycrystalline graphite, passing between gaps between atoms in slice that is similar size to wavelength of electrons so forms diffraction pattern at end of tube (rings)
- WAVE behaviour
when they hit screen with impact - PARTICLE behaviour
de Broglie wave equation
wavelength of particle inversely proportional to its momentum
𝝀=h/p
