- perfect gas
- perfect inelastic collision
- perfect optical system
- period
- periodicity
- periscope
- permanent magnet
- permeability
- permeability of vacuum
- permeameter
- permittivity
- permittivity of vacuum
- permittivity tensor
- permutation group, symmetric group
- permutation operator
- perpendicular axis theorem
- perturbation
- perturbation theory
- perturbing potential
- Pfund series
- phase
- phase angle
- phase cell
- phase constant
- phase contrast
- phase diagram
- phase difference
- phase equilibrium
- phase factor
- phase grating
- phase jump
- phase shift
- phase shifter
- phase space
- phase transition
- phase velocity
- phase voltage
- phenomenological theory
- phenomenon
- phonometer
- phosphorescence
- photo-conductive effect
- photo-electron
- photocurrent
- photoelasticity
- photoelectric cell
- photoelectric effect
- photoelectric tube
- photography
- photoluminescence