Chapter 19: Electric Fields

Capacitor

An electrical device that stores charge, consisting of two conductors (plates) separated by a vacuum or dielectric.

Dielectric

An insulating material placed between capacitor plates that increases its capacitance.

Capacitance (C)

The amount of charge stored per unit of potential difference between a capacitor’s plates, measured in farads (F).

Capacitance Formulas

Basic Formula

$C=\frac{Q}{V}$, where Q is the charge and V is the potential difference.

Dielectric Formula

$C=\kappa C$₀ , where κ is the dielectric constant and C₀ is the capacitance with a vacuum.

Key Properties

• Capacitance increases with the plate area (A).
• Capacitance decreases with increasing plate separation (d).
• Dielectrics enhance capacitance by reducing the electric field between plates.

Capacitors in Circuits

Parallel Configuration

The total capacitance is the sum of individual capacitances: $C$_total = C ₁ + C ₂ + ... .

Series Configuration

The total capacitance is given by: $\frac{1}{C}$_total = 1 C ₁ + 1 C ₂ + ... .

Applications

• Energy Storage: Capacitors store charge for later use in circuits.
• Filters: Capacitors smooth voltage fluctuations in power supplies.
• Defibrillators: Devices that use capacitors to deliver controlled electrical shocks.

Questions for Students

1. Define capacitance and its SI unit.
2. Explain how a dielectric affects a capacitor's properties.
3. Calculate the total capacitance for capacitors in parallel and in series.
4. Describe a practical application of capacitors in daily life.
5. Determine the charge stored in a 2.0 μF capacitor at a potential difference of 5.0 V.