Online Physics Glossary / Terms / Dictionary

# Physics Definitions Start from E

Electromagnetic Force - Model of the atom proposed by Neils Bohr in 1913. It showed electrons in fixed orbits around the nucleus, but acting in some ways like waves.

Electromagnetic Radiation - Radiation that travels through vacuous space at the speed of light and propagates by the interplay of oscillating electric and magnetic fields. This radiation has a wavelength and a frequency.

Electromagnetic Spectrum - The entire range of all the various kinds or wavelengths of electromagnetic radiation, including (from short to long wavelengths) gamma rays, x-rays, ultraviolet, optical (visible), infrared, and radio waves.

Electron - A negatively charged elementary particle that normally resides outside (but is bound to) the nucleus of an atom.

Electron Cloud Model - Scientific machine in which particles are accelerated as they travel around a circular path.

Electron Flux - The rate of flow of electrons through a reference surface. In cgs units, measured in electrons s-1, or simply s-1.

Electron Volt - Abbreviated eV. A unit of energy used to describe the total energy carried by a particle or photon. The energy acquired by an electron when it accelerates through a potential difference of 1 volt in a vacuum. 1 eV = 1.6 x 10-12 erg.

Electron Volt (eV) - Attraction or repulsion due to the electric charge of matter.

Energy Flux - The rate of flow of energy through a reference surface. In cgs units, measured in erg s-1. Also measured in watts, where 1 watt = 1 x 107 erg s-1. Flux density, the flux measured per unit area, is also often referred to as "flux".

Erg - A cgs unit of energy equal to work done by a force of 1 dyne acting over a distance of 1 cm. 107 (ten million) erg s-1 (ergs per second) = 1 watt. Also, 1 Calorie = 4.2 x 1010 (42 billion) ergs.

Effective Current - DC current that would produce the same heating effects.

Effective Voltage - DC potential difference that would produce the same heating effects.

Efficiency - Ratio of output work to input work.

Effort Force - Force extended on a machine.

Elastic Collision - Interaction between two objects in which the total energy is the same before and after the interaction.

Elasticity - Ability of object to original shape after deforming forces are removed.

Electrical Charge Pump - Device, often a battery or generator, that increase potential of electrical charge.

Electrical Circuit - Continuous path through which electrical charges can flow.

Electrical Current - Flow of charged particles.

Electrical Field - Property of space around a charged object that causes forces on other charged objects.

Electric Field Lines - Lines representing the direction of electric field.

Electric Field Strength - Ratio of force exerted by field on a tiny test charge to that change.

Electric Generator - Device converting mechanical energy into electrical energy.

Electric Potential - Ratio of electric potential energy to charge.

Electric Potential Difference - Difference in electric potential between two points.

Electric Potential Energy - Energy of a charged body in an electrical field.

Electromagnet - Device that uses an electric current to produce a concentrated magnetic field.

Electromagnetic Induction - Production of electric field or current due to change in magnetic flux.

Electromagnetic Radiation - Energy carried by electromagnetic waves throughout space.

Electromagnetic Waves - Wave consisting of oscillating electric and magnetic fields that move at speed of light through space.

Electromotive Force - Potential difference produced by electromagnetic induction.

Electron Cloud - Region of high probability of finding an electron around an atom.

Electron Diffraction - Effects on electrons due to wave-like interference of electrons with matter.

Electron Gas Model - Description of current flow through conductors.

Electroscope - Device to detect electric charges.

Electrostatics - Study of properties and results of electric charges at rest.

Electroweak Force - Unification of electromagnetic and weak forces.

Elementary Charge - Magnitude of the charge of an electron. 1.602 *10^ -19

Emission Spectrum - Spectrum produced by radiation from excited atoms.

Energy - Non-material property capable of causing changes in matter.

Energy Levels - Amounts of energy an electron in an atom may have.

Entropy - Measure of disorder in a system; ratio of heat added to temperature.

Equilibrant Force - Force needed to bring an object into transitional equilibrium.

Equilibrium - Condition in which net force is equal to zero. Condition in which net torque on object is zero.

Equivalent Resistance - Single resistance that could replace several resistors.

Evaporation - Change from liquid to vapor state.

Excited State - Energy level of atom higher than ground state.

External Forces - Forces exerted from outside a system.

Extrinsic Semiconductor - Semiconductor in which conduction is primarily the result of added impurities.