Past exam of the physics course of the year 1 of the natural sciences course of the University of Cambridge / 2011 / Paper 1 / Section A / A2 / Solution

By symmetry, the two grounded plates take equal induced surface charge and the electric field has magnitude $\sigma /(2{ϵ}_0)$ between either plate and the sheet. The grounded-plate potential of a central charged sheet is thereforeAn electron released at zero potential gains kinetic energy $e{V}_{\mathrm{sheet}}$. ThusThe planar infinite-sheet approximation neglects edge effects. Here $e>0$ denotes charge magnitude; the electron's negative charge makes it accelerate toward the positive sheet. Relativistic corrections are below0.1%. Numerical constants use rounded CODATA values, not a claim about the historical handbook: ${ϵ}_0=8.85419\times 10^{-12}\mathrm{F}{\mathrm{m}}^{-1}$, $e=1.602176634\times 10^{-19}\mathrm{C}$ and $m_e=9.10938\times 10^{-31}\mathrm{kg}$. ^[ref]