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Electricity and Magnetism Electric Fields Coulomb’s Law The force between two charges is directly proportional to their magnitudes and inversely proportional to the square of the distance between them.
This law has been verified by experiment. The constant of proportionality depends on the medium.
The constant e is called the permittivity of the medium. If the medium is a vacuum the constant is written eo. The units of e are N-1C2m-2, (this is usually written as Farads per metre, Fm-1). Electric Field Strength (E) The electric field strength at a point is the force acting on a unit positive charge placed at that point.
Electric Field Strength at a distance r from a Point Charge Q
To calculate the field strength at point p, imagine a 1C (positive) charge to be placed at p and then use Coulomb’s law.
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© David Hoult 2008 |
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