Two large parallel thin plates having uniform charge densities `+ sigma and - sigma` are kept in X-Z plane at a distance d apart. Sketch an equipotential surface due to electric field between the plates. If a particle of mass m and charge `-q` remains stationary between the plates, what is the magnitude and direction of the filed ?

Explanation

In fig, we have shown the electric field lines by solid line curves with arrowheads. The corresponding surfaces are shown by dotted curves.

If E is magnitude of the filed between th plates, then as particle remains stationary,
upward force due to electric filed = wieght of paricle
`-qE = mg`
`E = -(mg)/(q)`
The direction of filed is downwards, i.e, along negative Y-axis.