I

Iapetus - satellite of Saturn (discovered 1671)
ice - solid form of water
ice pail - device to show equality of charge produced in electrostatic induction
ideal gas - one which obeys Boyle's Law
igneous rock - rock formed directly from solidifying from its molten state
illuminate - shine light on something
image - point to which rays converge (real) or from which they appear to diverge (virtual)
image distance - the distance between the image and the lens or mirror that forms it
impedance - in an a.c circuit the ratio of the RMS e.m.f. in a circuit to the RMS current flowing
impulse - force x time for which the force is acting. Results in a momentum change.
incandescent - substances that give out light when raised to high temperatures (say > 800^oC)
incidence - incoming; angle of incidence - between incoming ray and the normal
inclined - sloping, as in an 'inclined plane'
inclinometer - instrument for measuring magnetic field inclination (dip)
induction - production of a charge or voltage by an external change
induction coil - device for producing high voltage
inelastic - a collision where all the kinetic energy is converted to other forms
inertia - the reluctance of a body to change its state of motion
inertia balance - apparatus for showing inertia, difference between mass and weight (wig-wag)
inertial mass - mass defined using Newton's Second Law, F = ma
inert gas - one consisting of atoms that are chemically inactive and rarely bond with others
inferior planets - Mercury and Venus. Those between the Earth and the Sun.
infra red - electromagnetic radiation with a wavelength a little longer than red
initial - original, starting, as in 'initial velocity'
insoluble - something that will not dissolve
insulator - material that will not transfer heat energy or electrical energy by particle vibration
interaction - reacting with and affect each other involving forces, as in 'particle interaction'
interface - the boundary or join between two parts
interference - overlapping of two waves to give a combined pattern
interferometer - device for measuring distances using an interference pattern
internal - inside, as in 'internal energy' and 'internal resistance'
internal resistance - resistance of the power source itself, as in cell, power supply or dynamo
interstellar - between the stars, as in 'interstellar matter'
inferior planets - planets closer to the Sun than the Earth, Mercury and Venus
insulator - material that prevents (or reduces) conduction of heat or electricity
intrinsic semiconductor - one with no added impurities, e.g. pure germanium or silicon
intensity - brightness or strength, as in 'the intensity of a light' or 'intensity of a field'
inverse square law - law where the force is proportional to the inverse square of the distance
inversion - reversal of the normal, as in 'population inversion' of electrons in an atom
inverted - upside down
Io - moon of Jupiter with the only active volcano known outside Earth
ion - a charged atom or molecule (can be positive or negative)
ionisation - process of forming ions
iris - coloured part at the front of the eye, controls the amount of light entering the eye
isobar - line on a map joining points of equal atmospheric pressure
isobaric - a change that takes place without change of pressure
isochronous - same time, as in the period of the swing of a given pendulum
isothermal - changes in a gas that take place at a constant temperature
isotones - nuclides with the same neutron number
isotopes - nuclei with the same number of protons but different numbers of neutrons