Question

Two concentric conducting thin spherical shells $A$ and $B$ having radii $r_A$ and $r_B\left(r_B>r_A\right)$ are charged to $Q_A$ and $Q_B\left(\left|Q_B\right|>\left|Q_A\right|\right)$. The electrical field along a line (passing through the centre) is

• A.
• B.
• C.
• D.

Answer 1

Answer: (A)

The electric field inside the shell $A$ is zero.

At the surface of shell $A,E_A=\frac{k{Q}_A}{r_A^2}$
Between the shell $A$ and $B$, at a distance $x$ from the common centre,
$E=\frac{k\cdot Q_A}{x^2}$ towards right, hence positive At the surface of shell $B,E_B=\frac{k\cdot Q_A}{r_B^2}$ towards right hence positive.
Outside both the shells, at a distance $x$ from the common centre, $E_{\text{out }}=\frac{k\left(Q_A-Q_B\right)}{x^{\prime 2}}$, towards left,