Question

Three conducting plates, each of thickness, d, and surface area, A, are placed one above the other with surfaces horizontal. The plates are equally spaced, with the gap between each parallel set of surfaces also being equal to d. Potential differences are placed across the plates resulting in a net charge of −4Q on the middle plate, +Q on the lower plate and +3Q on the upper plate. Ignore edge effects in answering each of the following.

(a) Discuss the charge distribution that you would expect to eventuate on the surfaces of each conducting plate, and determine expressions for the fields between the plates assuming that the fields in each region are constant. Ensure you specify field magnitudes and directions.

(b) By integrating the electric field, determine an expression (or expressions) and make a plot of the electrical potential as a function of height, y, from the bottom plate up to the top plate. Assume that the potential on the bottom plate is zero.

(c) Suppose that the spacing between the plates was increased. Discuss the effect on the energy stored in the plates for the following situations:

(i) The charge on the plates is kept constant.

(ii) The potential difference between the plates is kept constant.

Answer 1