              home  physics online guide physics help my info terms of use contacts    What is Physics? Mechanics Electricity and Magnetism Electric Field Gauss' Law about below subjects Electric Potential Capacity Direct Current Magnetic Field Magnetic Field Laws Magnetic Interactions Electromagnetic Induction Maxwell's Equations Oscillations and Waves Simple Harmonic Motion Damped Harmonic Motion Driven Harmonic Motion Electric Oscillation Alternating Current Wave Motion Elastic Waves Electromagnetic Waves Optics Light Waves Geometrical Optics Interference Polarization Diffraction Fraunhofer Diffraction Dispersion, Absorption, Diffusion Doppler Effect Thermodynamics Ideal Gas Molecular Statistics Transport Phenomena First Law of Thermodynamics Second and Third Laws of Thermodynamics Imperfect Gas Liquids Solids Quantum Physics Thermal Radiation Quantum Properties of Light Wave Properties of Particles Planetary Model of Atom X-Rays Particle in Potential Well Pauli Exclusion Principle Nuclear Physics Solid State Physics Appendices  # Electric Field   full version SI units & Physics constants

Electricity is the branch of physics, which investigates interactions between electric charges Here (all units see here): is electric force on charge q from Q is electric force on charge Q from q is position vector of charge q with respect to Q is electric field produced by charge Q near q

## General formulas

Point charge is a charge which dimensions are small with respect to distance between the charge and the point where the electric field from this charge is defined

The electric force vector between two point charges is defined by Coulomb’s law where is permittivity of vacuum Another form of Coulomb's law where is Coulomb constant

The magnitude of electric force or ## Electric Charges

The electric charge of object is a scalar value given by where:

Np and Ne are numbers of protons and electrons in the object

## Charge Conservation Law

The Charge Conservation Law states that in any isolated system the net charge remains constant where n is total number of charges in the system

## The electric field

The electric field vector is defined by The magnitude of electric field The electric field produced by point charge Q at a distance from the charge Magnitude of electric field  Here P is a point where the electric field is defined

## Electric field lines

Any electric field can be defined graphically by means of the electric field lines, as shown below The electric field lines are drawn as curves so that the tangent line to the curve at arbitrary point P is directed along the vector of the electric field at this point, and the density of lines is directly proportional to the magnitude of the electric field where:

N is the number of lines crossing a small area A, oriented normally to the electric field with the center at the point P

s is scale coefficient, which is the same for all points

The electric field lines from point charge   where is area of sphere with radius r  and center at the charge Q

## Uniform electric field

The uniform electric field is electric field where the vector is constant everywhere in magnitude and direction  ## Superposition Principle

The Superposition Principle states that net electric field produced at any point by a system of charges is equal to the vector sum of all individual fields, produced by each charge at this point where n is total number of charges in the system

The Superposition Principle for two point charges where and are position vectors of point P with respect to the charges Q1 and Q2 respectively The Superposition Principle for system of n point charges where is position vector of point P with respect to the charge for i = 1, 2, 3,..., n

The Superposition Principle for charge continuously distributed over an object where: is radius position of point where the electric field is defined with respect to small volume dV with volume charge density V is volume of the charged object

Electric field produced by uniformly charged ring at its axis with magnitude where: is radius position of point P where the electric field is defined with respect to center of the ring

Q is total charge of the ring  home  |  physics online guide  |  physics help  |  my info  |  terms of use  |  contacts Dr. Nikitin © 2010       