PhysicsChapter 5: Electric Potential and Capacitor
Parallel-Plate Capacitor
A parallel-plate capacitor
Definition
A parallel-plate capacitor consists of two conducting plates of area `A`, separated by distance `d`, with capacitance in vacuum approximately: C = ε₀A/d when edge effects are neglected.
Formula
C = ε
Dependence
For plate charge magnitude `Q`: surface charge density: σ=QA Between large oppositely charged plates: E≈σε₀ Thus: E=Qε₀A Potential difference: V=Ed so: V=Qd/(ε₀A) From: C=QV we get: C=ε₀A/d Area increases: **C increases Plate separation increases: C decreases**
With Dielectric
If a dielectric of relative permittivity `κ` completely fills the space: **C=κε₀A/d** under the usual ideal model.
Formula / Key Relation
**C=ε₀A/d With dielectric: C=κε₀A/d**
Exam preparation
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Review the key facts, formulas and checks before you move on.Parallel-Plate Capacitor
Sticky Notes · Quick Revision
Parallel plates:
- `C=ε₀A/d`
- Bigger A → bigger C
- Bigger d → smaller C
60-second revision
- Geometry controls capacitance.
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