Two concentric coducting thin spherical shells A and B having radii `r_A` and `r_B(r_Bgtr_A)` are charged to `Q_A` and `-Q_B(|Q_B|gt|Q_A|)`. The electrical field along a line passing through the centre is

Options

A.
B.
C.
D.

Answer

a

Explanation

The electric field inside the shell `A` is zero

At the surface of shell `A, E_(A)=(kQ_(A))/(r_(A)^(2))`
Between the shell `A` and `B`, at a distance `x` from the common centre
`E=(k.Q_(A))/(x^(2))` towards right hence positive
At the surface of shell `B, E_(B)=(k.Q_(A))/(r_(B)^(2))` towards right hence positive. Outside the both shell, at a distance `x` from the common centre `E_(out)=(k(Q_(A)-Q_(B)))/(x'^(2))`
hence negetive(as `x'` increases negative value of `E_(out)` decreases and it becomes zero at `x= oo`)