18.5.2—The fact that the electric field at a point is equal to the negative of

Electric field strength points in the direction of decreasing electric potential; in one dimension E=−dV/dr.

The minus sign links field direction to potential fall. In a uniform field, the gradient is constant; near a point charge it changes with distance.

A potential drop of 20 V over 0.010 m in the field direction corresponds to E≈2000 N C⁻¹.

Electric field is not potential itself; a high potential region can have zero field if potential is locally constant.