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 × 10³N/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,

E= 1 /4πε₀   x   q/d²

Where, q = Net charge = 1.5 x 10³ N/C

d = Distance from the centre of sphere = 20 cm = 0.2 m

ε₀  = Permittivity of free space and

1 /4πε₀ = 9 x10⁹Nm²C⁻²

Therefore,

q = E(4πε₀)d² =

=(1.5 x 10³) (0.2)² / (9 x 10⁹)

6.67 x 10⁻⁹C =6.67 nC

Therefore, the net charge on the sphere is 6.67 nC.