Question

We have an isolated conducting spherical shell of radius 10 cm. Some positive charge is given to it so that 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 20 cm. Now, first shell is placed inside the second so that both are concentric as shown in the figure.
The electric field intensity just inside the outer sphere is

• A. $4.5\times {10}^{5}N/C$
• B. $9\times {10}^{5}N/C$
• C. $4.5\times {10}^{4}N/C$
• D. $5\times {10}^{5}N/C$

Answer 1

The correct option is A $4.5\times {10}^{5}N/C$

Let q be the charge given to shell of radius 10 cm. So, the charge given to shell of radius 20 cm.
We know that the maximum electric field intensity is at the surface of shell
$⟹1.8\times {10}^{6}N{C}^{-1}=\frac{kq}{(0.1{)}^2}$
$⟹kq=1.8\times {10}^{4}N{m}^2{C}^{-1}$
We must know that the electric field just inside the outer shell will only be due to the inner shell.
$⟹E=\frac{kq}{(0.2{)}^2}$
$\therefore E=4.5\times {10}^5$ $N{C}^{-1}$