Electric fields

• Coulomb's law states that the magnitudes of the forces between two point charges in a vacuum is directly proportional to the product of their charges, and inversely proportional to the square of the distance between the charges.
• The constant, k, in coulombs law equation equals one over four multiplied by pi multiplied by the permittivity of free space.
• The force between two point charges equals kQq/r^2.
• Charge may be presumed to act at the centre of a charge and therefore r is the distance between the centres of the charges.
• If charges have the same sign, the force will be repulsive, and if the charges have different signs, the force will be attractive. Therefore a positive force is repulsive and a negative force is attractive.
• Electric field strength (E) is the force per unit charge experienced by an object in an electric field.
• The general equation for electric field strength is E=F/Q.
• The equation for electric field strength for uniform fields is E=V/d.
• The equation for electric field strength for a radial fields is E=kQ/r^2.
• The work done moving a charged particle in a uniform field equals charge multiplied by the change in potential difference.
• Electric potential (V) at a point is the work done per unit charge moving an object from infinity to that point. The potential at infinity is zero.
• The equation for potential (in a radial field) is V=kQ/r.
• The equation for electric field strength using potential is E=delta V/delta r.
• Electric potential difference is the energy needed to move a unit charge between two points.
• An electric field acts on any charged object and can be attractive or repulsive.