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Physics Definitions Start from I

Intensity Map - A color-coded map of radiation intensity as a function of position. Different colors or shades represent different intensities of observed radiation.

Ion - An atom that has lost or gained one or more electrons and has become electrically charged as a result.

Ionization - The process by which ions are produced, typically occurring by collisions with atoms or electrons ("collisional ionization"), or by interaction with electromagnetic radiation ("photoionization").

Ionosphere - The region of the Earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoionization of the constituents of the atmosphere by solar ultraviolet radiation. The ionosphere significantly influences radiowave propagation of frequencies less than about 30 MHz.

Isotope - One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.

Ideal Mechanical advantage - In simple machine, the ratio of effort distance to resistance distance.

Illuminance - Rate at which electromagnetic wave energy falls on a surface.

Illuminated Object - Object on which light falls.

Image - Reproduction of object formed with lenses or mirrors.

Impulse - Product of force and time interval over which it acts.

Impulse-momentum Theorem - Impulse given to an object is equal to its change in momentum.

Incandescent Body - Object that emits light because of its high temperature.

Incident Wave - Wave that strikes a boundary where it is either reflected or refracted.

Incoherent Light - Light consisting of waves that are not in step.

Independent Variable - Variable that is manipulated or changed in an experiment.

Index of Refraction - Ratio of the speed of light in vacuum to its speed in a material.

Inelastic Collision - Collision in which some of the kinetic energy is changed into another form.

Inertia - Tendency of object not to change its motion.

Inertial Mass - Ratio of net force exerted on object to its acceleration.

Initial Velocity - Velocity of object at time t=0.

Instantaneous Acceleration - Acceleration at a specific time; slope of tangent to velocity- time graph.

Instantaneous Position - Position of an object at specific time.

Instantaneous Velocity - Slope of the tangent to position- time graph.

Insulator - Material through which the flow of electrical charge carriers or heat is greatly reduced.

Interference Fringes - Pattern of dark and light bands from interference of light waves.

Interference of Waves - Displacements of two or more waves, producing either large or smaller waves.

Internal Forces - Forces between objects within a system.

Intrinsic Semiconductor - Semiconductor in which conduction is by charges due to host material, not impurities.

Inverse Relationship - Mathematical relationship between two variables, x and y, summarized by the equation xy=k, where k is a constant.

Ionizing Radiation - Particles or waves that can remove electrons from atoms, molecules, or atoms in a solid.

Isolated System - A collection of objects not acted upon by external forces into which energy neither enters nor leaves.

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