A 10 cm sphere carries charge 1 μC. The field magnitude at 30 cm from its centre is

1. At r = 0.3 m we are outside the sphere so E = q/(4πε₀r²). 2. Substitute q = 10⁻⁶ C, 1/(4πε₀) = 9×10⁹: E = (9×10⁹ × 10⁻⁶)/(0.3)². 3. E = 9×10³/0.09 = 10⁵ N/C. _Source: Maharashtra Balbharati Std XII Physics, Ch 8 "Electrostatics" §8.2.1 Example 8.1_