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## Homework Statement

The negative plate of a charged, isolated parallel plate capacitor with a vacuum gap of width d and carrying a surface charge density s is uniformly irradiated with a short pulse of ultraviolet light whose photon energy is just enough to release a photoelectron at the surface with zero kinetic energy. The radiant energy per unit area deposited by the pulse is such that a photoelectron surface charge density of exactly s is generated. Derive an expression for t_van, the time taken following the ultraviolet pulse for the electric field to vanish everywhere between the plates. Evaluate t_van for s=0.1 micro Coulomb per unit area and d=1mm

## Homework Equations

None given

## The Attempt at a Solution

I'm very confused by the question, I'm really not sure which equations to use. Presumably, the photoelectron would produce an electric field which would interfere with the two plates, but does this mean I use the equations for polarisation? Thanks in advance.