21)
We thus arrive at two important conclusions concerning the relation
between electric field and potential:
(i)
Electric field is in the direction in which the potential decreases
steepest (ii) Its magnitude is given by the change in the magnitude of potential
per unit displacement normal to the equipotential surface at the point 2 7  POTENTIAL ENERGY OF A SYSTEM OF CHARGES
Consider first the simple case of two charges q1and q2 with position vector
r1 and r2 relative to some origin