Ideal gas – a gas made up of a large number of small spherical molecules, in random motion , that have only elastic collisions

Ideal gas law – the product of the pressure and the volume, for a fixed amount of gas, is proportional to the absolute temperature ( see equation 12.4 and Section 12.5)

Image distance – the distance of the image from the lens

Impedance – the factor that relates the peak voltage to the peak current, represented by Z in equations (see equation 21.21)

Impulse – the product of force and the time interval over which the force acts

Impure (extrinsic) semiconductors – semiconductors to which small numbers of impurity atoms have been added thereby altering their conductivity

Index of refraction – the ratio of the speed of light in a vacuum to the speed of light in the specified medium

Induced current – current produced in a conductor by a changing magnetic flux

Induced emf – the potential difference produced in a conductor by a changing magnetic flux

Inductance – the magnetic flux produced per unit current in a coil (see equation 20.8)

Inductive reactance – in an AC circuit, the voltage across the coil (inductor) divided by the current through the coil; analogous to resistance in a DC circuit (see equation 21.19)

Inductive time constant – in a circuit with an inductor (coil) and a resistor, the time required for the current to rise to 37% (1/e) of its final value (see equation 21.3)

Inductor – a circuit component that exhibits inductance and acts to resist change in current

Inelastic collision – a collision in which kinetic energy is not conserved

Inertia – the property of matter that causes objects to resist changes in motion

Inertial reference frame – a reference frame in which Newton’s first law is valid

Infrared – the region of the electromagnetic spectrum between microwaves and visible light

Insulator - a material through which charge flows poorly or not at all

Instantaneous acceleration – acceleration at any particular instant of time, the limiting value of Dv/Dt as the time interval (Dt) becomes vanishingly small

Instantaneous angular acceleration – angular acceleration at any particular instant of time, the limiting value of Dw/Dt as the time interval (Dt) becomes vanishingly small

Instantaneous velocity – velocity at any particular instant of time, the limiting value of Dx/Dt as the time interval (Dt) becomes vanishingly small

Intensity – the power flowing through unit area

Intensity level – in decibels, ten times the logarithm (in base 10) of the ratio of the intensity to a reference intensity (see equation 15.5)

Internal energy – total kinetic energy and potential energy associated with the internal state of the atoms composing a thermodynamic system (see equation 12.8)

International System of Units – (SI) units based on the metric system of measurements

Inverse-square force – a force proportional to the reciprocal of the square of the distance

Inverted population – the state of having more ions in the upper state (energy level) than in the lower state

Isobaric process – a process during which there is no change in pressure of the system

Isochoric process – a process during which there is no change in volume of the system

Isothermal process – a process during which there is no change in the temperature of the system

Isotope – atoms of an element that have different numbers of neutrons and therefore different atomic mass numbers