Solutions
247electric field strength at point (^0) produced by the
surface element AS is given by
I a
AE = (^) AS cos cp
47E5 (^0) R 2
where q is the angle between the normal to the
area element and the vertical. But_AS cos q is the
Fig. 207
4neo R 2
where S is the area of the hatched figure in Fig. 207,
which is the projection of the lobule on the hori-
zontal plane zOy. Since the area of any narrow
strip of this region (black region in Fig. 207) is
smaller than the area of the corresponding strip
of the large circle by a factor of sin (a/2), the entire
area of the projection of the element AS on the
horizontal plane. Hence the total field strength
at point 0 can be determined from the formula
I QS
E' =