Question

The dielectric strength of air is $2.0\times10^6 N/C$. The largest charge that a metallic sphere of $3 \,mm$ radius can hold is

• A. 2 $n$C
• B. 3 $n$C
• C. 1.5 $n$C
• D. 6 $n$C

Answer 1

Answer: (A)

2 $n$C

Answer 2

Electric field on the surface of the sphere should not exceed $2.0 \times 10^6$ N/C. $\therefore$ $9 \times 10^9 \times \frac{q}{(4 \times 10^3)^2} = 2.0 \times 10^6$ This gives $q = 2 \times 10^9$ C.