Fig 1.17 : Gradient of a scalar function
As shown in figure 1.17, let us consider two surfaces S1and S2 where the function V has constant magnitude and the magnitude differs by a small amount dV. Now as one moves from S1 to S2, the magnitude of spatial rate of change of V i.e. dV/dl depends on the direction of elementary path length dl, the maximum occurs when one traverses from S1to S2along a path normal to the surfaces as in this case the distance is minimum.