# A spherical conductor of radius 10 cm has a charge of 3.2×10-7C distributed uniformly. What is the magnitude of electric field at a point 15cm from the centre of the sphere? (1/4π∈0= 9 × 109Nm/C2) (1) 1.28 × 105 N/C (2) 1.28 × 106 N/C (3) 1.28 × 107N/C (4) 1.28 × 104 N/C

Answer: (1) 1.28 × 105 N/C

Given:

• The charge present inside the sphere (q) = 3.2×10-7C
• The electric field is to be determined at a point at r = 15cm

Because the point is outside the sphere, the electric field can be calculated by considering a point charge of the same magnitude 15 cm away from the sphere, because the entire charge is concentrated at the centre.

$$\begin{array}{l}Electric,feild(E) =frac{1}{4pi epsilon _{0}}frac{q}{r^{2}}\end{array}$$

Substitute the given value

$$\begin{array}{l}E = 9times 10^{9}times frac{3.2times 10^{-7}}{0.0225}\end{array}$$

E = 1.28 × 105 N/C