A spherical conductor of radius 10 cm has a charge of 3.2 × 10-7 C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere ?
$\left({1\over4\pi\epsilon_0}=9×10^9 N m^2/C^2\right)$
(1) 1.28 × 107 N/C
(2) 1.28 × 104 N/C
(3) 1.28 × 105 N/C
(4) 1.28 × 106 N/C