VCE · Topic explainer
Electron kinetic energy between charged plates
A charge accelerated across a potential difference gains kinetic energy equal to the magnitude of charge multiplied by the voltage, if electric work is the only energy transfer. An electron accelerated through one volt gains one electronvolt. Plate spacing affects the field strength for fixed voltage.
Worked example
An electron starts nearly at rest and is accelerated through 120 V. Its kinetic energy increases by 120 eV, or about 1.92 × 10⁻¹⁷ J. This uses the full potential difference between its start and finish.
Double the spacing while holding the voltage fixed. In an approximately uniform field, E = V/d, so the field strength halves. The force acts over twice the distance, so the gain in kinetic energy across the full gap is the same.
Official exam practice
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