Parallel plate capacitor
A device consisting of two parallel conducting plates separated by a small distance, used to store electrical charge and energy. Capacitance C = ε₀εᵣA/d where A is plate area, d is separation, ε₀ is permittivity of free space, and εᵣ is relative permittivity of the dielectric.
Formula
C = ε₀εᵣA/d
Real World
The touchscreen on an iPhone uses a grid of parallel-plate-style capacitors; when your finger approaches, it alters the local capacitance, and the phone's processor pinpoints exactly where you touched.
Exam Focus
When comparing two capacitors, write the ratio C₁/C₂ explicitly — examiners penalise vague statements like 'capacitance increases' without quantitative justification.
How well did you know this?