General fields

• A field is an area in which an object experiences a non-contact force.
• Fields can be represented by vectors which describe the direction the force acts in.
• Fields can be represented on diagrams by field lines, on which an arrow shows the direction and the relative distance between the lines shows the strength of the field.
• A uniform field is one where the field acts in the same direction with the same strength across the whole area.
• A radial field is one where the field lines extends out from the centre of the object in all different directions, and the further away the weaker the force.
• Very close to the surface of a large object, a radial field can be assumed to be uniform.
• Equipotential surfaces are where the potential is constant everywhere on the surface, ie the field has the same strength and no work is done moving along it.
• Air may be presumed to be a vacuum.
• The magnitude of electrostatic forces between subatomic particles are many magnitudes larger than the magnitudes of the gravitational forces as their charges are are much larger than their masses. Therefore, gravitational force can be considered to have a negligible effect.