Definitions Glossary

Term	Definition	Formula / Value	Unit
Photoelectric effect	Emission of electrons from a metal surface when incident light has frequency ≥ ν_{0}	—	—
Photon	Discrete quantum (particle) of electromagnetic radiation carrying energy hν and momentum h/λ	E = hν; p = h/λ	J; kg·m/s
Planck's constant (h)	Fundamental constant relating photon energy to frequency	h = $6.63 \times 10^{-34}$ J·s	J·s
Work function (φ)	Minimum energy required to eject an electron from a metal surface	φ = hν_{0}	J or eV
Threshold frequency (ν_{0})	Minimum frequency of incident light for photoelectric emission	ν_{0} = φ/h	Hz
Threshold wavelength (λ_{0})	Maximum wavelength of incident light for photoelectric emission	λ_{0} = hc/φ	m or nm
Stopping potential ( $V_{0}$ )	Minimum retarding potential that reduces photocurrent to zero	e $V_{0}$ = KE_max = hν − φ	V (volt)
Saturation current	Maximum photocurrent; occurs when all emitted electrons reach collector	I_sat ∝ intensity	A
KE_max (maximum KE of photoelectrons)	Kinetic energy of the most energetic photoelectrons (from the surface, no energy loss)	KE_max = hν − φ	J or eV
Einstein's photoelectric equation	Energy conservation equation for the photoelectric effect	KE_max = hν − φ	J
de Broglie hypothesis	Proposal that every moving particle has an associated matter wave	λ = h/mv = h/p	m
de Broglie wavelength (λ)	Wavelength associated with a moving particle of momentum p	λ = h/p	m
Matter waves	Wave-like properties associated with moving particles (electrons, protons, etc.)	λ = h/mv	m
Davisson-Germer experiment	1927 experiment confirming electron diffraction from Ni crystal at 54 V, 50°	Verified λ = h/√(2meV)	—
Wave-particle duality	The property of quantum entities (photons, electrons) exhibiting both wave and particle behavior	—	—
Photocurrent	Electric current produced due to flow of photoelectrons in the circuit	I ∝ n × e (n = electrons/sec)	A
Thermal de Broglie wavelength	de Broglie wavelength for particles at thermal equilibrium at temperature T	λ = h/√(3mkT)	m
1 eV	Energy gained by an electron moving through 1 volt potential difference	1 eV = $1.6 \times 10^{-19}$ J	J