As indicated above, this is the scalar component of the curl in the z direction since the normal ^n to ΔxΔy is in the
positive z direction.
The other two components are obtained in exactly the same manner. We give them here without repeating the process
(see Exercise 2.9). The scalar component of the curl in the x direction is obtained by finding the total circulation around the
loop a0d0c0b0a0 in the y–z plane in Figure 2.22 and then taking the limit in Eq. (2.87):