Capacitor & Dielectric – AP Physics C E&M | ShowMeClass

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Capacitor & Dielectric

AP Physics C E&M · Unit 3: Capacitance

Learning Objectives

Calculate C for parallel plates

Analyze effect of dielectric on C, E, V

Calculate stored energy U = 1/2 CV2

Combine capacitors in series/parallel

Key Equations

Dielectric Effect

Inserting a dielectric with constant κ:

C' = κC (capacitance increases)
E' = E/κ (field decreases)
V' = V/κ (voltage decreases, if Q fixed)

Colors

+ plate

- plate

Dielectric slab

E-field lines

CapacitorDielectricEnergy

C =-

Q =-

V =-

U =-

C, Q, U vs DIELECTRIC CONSTANT

Mode

Plate Area A (cm2) 100

Separation d (mm) 2.0

Applied V (V) 100

Dielectric κ 1.0

Vacuum: 1.0 · Paper: 3.7 · Glass: 5-10 · Water: 80

Dielectric Fill (%) 100

Display

Capacitor Analysis

Quick Quiz▼

1. Inserting a dielectric (kappa > 1) into a capacitor at fixed V:

Increases C, increases Q stored Decreases C, decreases Q No change Increases C, decreases Q

2. Energy stored in a capacitor is:

CV 1/2 CV2 CV2 Q2/C

3. Parallel-plate capacitance C0 equals:

eps0 * A / d eps0 * d / A A * d / eps0 eps0 / (A * d)