- isothermal efficiency
- isothermal expansion
- isothermal flow
- isothermal magnetization
- isothermal room
- isotonic
- isotope effect
- isotope separator
- isotopic abundance
- isotopic invariance
- isotropic dielectric
- isotropic noise
- isotropic radiation
- isotropic symmetry
- isotropism
- isovalent
- iterative impedance
- jacket space
- jacket water
- jet cooling
- jitter
- johnson noise
- jointing chamber
- jointless
- Jordan lag
- Josephson current
- Joule experiment
- jump scrolling
- jump vector
- junction capacitor
- junction detector
- junction point
- junction transposition
- K-factor
- K-meson
- keeping life
- Keldall effect
- kelvin
- kelvin effect
- Kelvin replenisher
- Kerr constant
- J factor
- jacketed vessel
- jammer
- jellium model
- jet compressor
- jet motor
- jet nozzle
- jet pump
- jet ventilation
- Johanson gauge
- joint pole
- joint valve
- justifying bit
- K-capture
- k-space
- Kapp vibrator
- kelvin bridge
- kelvin network
- kenetron
- Kerr shutter
- key switch
- keying
- kilogram-calorie
- kilovolts peak
- Josephson effect
- Josephson tunneling
- Joule cycle
- Joule heat
- joystick
- junction barrier
- junction circulator
- junction diode
- junction loss
- junction pole
- junction rectifier
- junction transistor
- justify
- K-level
- katadioptric
- Ketteler formula
- key
- keylock switch
- kilovolt-ampere
- Kirchhoff law
- Kirkwood gaps
- knee
- knife switch
- knockout
- Kerr effect
- key system
- keying wave
- kick back
- killer circuit
- kilocalorie
- kilovolt
- kilovoltmeter
- Kirchhoff formula
- Kirk cycle
- krypton lamp