Three inentical metal plates with large surface areas are kept parallel to each as shown in figure (30-E8). The leftmost plate is given a charge Q, the rightmost a chrge _2Q and the middle one remains neutral. Finde the charge appearing on the outer surface of the rightmost plate.

Explanation

Consider the gaussian surface the induced
charge be as shown in fig .
The nef field at p due to all the charge is
zero.
` (-2Q + q/2A(epsilon_0)) (left) + (q/2A (epsilon_0))(right)`
` + q - (q/2A(epsilon_0))(right) = 0 `
- 2 Q + q - Q + q = 0 `
q = 3/2 Q
charge on the side of right most plate
`= -2Q + q = -2Q + 3/2 Q `
` = - Q/2.`