Question

We have an isolated conducting spherical shell of radius $10cm$. Some positive charge is given to it so that the resulting electric field has a maximum intensity of $1.8\times {10}^{6}N{C}^{-1}$.The same amount of negative charge is given to another isolated conducting spherical shell of radius $20cm$. Now, the first shell is placed inside the second so that both are concentric as shown in figure. The electrostatic energy stored in the system is :

• A. $1.0J$
• B. $0.045J$
• C. $0.09J$
• D. $1.8J$

Answer 1

Answer: (C)

Let the charge on the shell of 10 cm radius is $Q$.
$E=\frac{Q}{4\pi {ϵ}_0(0.1{)}^2}\Rightarrow Q=1.8\times {10}^6\times 4\pi {ϵ}_0(0.1{)}^2$