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

Inside the shell A, electric field  
 

At the surface of shell A, 
  (a fixed positive value) 
Between the shell A and B, at a distance x from the common centre
  (asx increases E decreases)
At the surface of shell B,
  (a fixed negative value because  
Outside the both shell, at a distance x from the common centre 
  (asx' increases negative value of   decreases and it becomes zero at