Question 1.21: A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is 1.5 × 103 N/C and points radially inward, what is the net charge on the sphere?
Electric field intensity (E) at a distance (d) from the centre of a sphere containing net charge q is given by the relation,
q = Net charge = 1.5 × 103 N/C
d = Distance from the centre = 20 cm = 0.2 m ∈0 = Permittivity of free space
= 9 × 109 N m2 C−2
= 6.67 × 109 C = 6.67 nC
Therefore, the net charge on the sphere is 6.67 nC.