as the electrostatic force per unit positive charge that would act on a test charge placed at that point. So, generally,
throughout: a region of space
is: a vector field that gives rise to an electrical force on a test charge placed at any point in the region. [P3.1]
is defined: at any point specified by a position vector as the electrostatic force per unit positive charge that would act on a test charge placed at that point. So, generally,
whether the test charge 
is positive or negative. [P3.1, P3.2]
is related: to the electric potential by the requirement that it points in the direction of most rapid decrease of the potential, and has a magnitude given at every point by the magnitude of the rate of change of the potential in that direction (e.g. in the radial direction from an isolated point charge, so that 
). It therefore always points in a direction at right angles to lines or surfaces of equal potential, and from high potential towards low potential. [P3.1, P3.3]
has as its SI unit: the newton per coulomb 
or, equivalently, the volt per metre 
[P3.1, P3.3]
Copyright 1997, The Open University