Capacitance Demonstrations & notes

Warning Capacitors can act like High Voltage batteries, but more fatal! (unless it’s a flux capacitor)

Capacitor uses: 1. store energy for later use (like a battery) 2. Powerful discharge of current (spot welding, flash cameras) 3. Smooth/filter out current fluctuations (motors run better, less noise in sensitive circuits, less interference pick-up)

Basic Capacitor Extra + charge piles up on the left; other + charge is taken from the right

Dielectric adds capacitance C=  A/d  permitivity (polarizability)  = 1 air or vacuum 3 paper 10 glass 100 water 1000 ceramics

Types: paper Cheap <500V Low capacitance Sensitive to moisture

Types: ceramic Cheap Can handle 10kv Low capacitance robust

Types: electrolyte Polarized (if connect wrong, might explode!) <500V high capacitance Chemicals inside

Make your own

Capacitors stores energy in the E field Capacitance is a measure of the ability to store energy in the form of separated charges Capacitors take time to charge and discharge

Capacitance Equations Q = total charge Units: farads = C/V  0 = permittivity constant (C 2 /Nm 2) A = area of plate d = Distance between plates

Energy and Capacitors Equations

Capacitors in Series: same charge, share the voltage

Capacitors in Parallel Same voltage, but share the charge Q = Q 1 + Q 2 + Q 3 C P V = C 1 V + C 2 V + C 3 V C P = C 1 + C 2 + C 3

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