Formula and Equations For Capacitor and Capacitance

Electrical Technology

Capacitor and Capacitance Formulas and Equations

The following formulas and equations can be used to calculate the capacitance and related quantities of different shapes of capacitors as follow.

Table of Contents

Toggle

Capacitance of Capacitor:

The capacitance is the amount of charge stored in a capacitor per volt of potential between its plates. Capacitance can be calculated when charge Q & voltage V of the capacitor are known:

C = Q/V

Charge Stored in a Capacitor:

If capacitance C and voltage V is known then the charge Q can be calculated by:

Q = C V

Voltage of the Capacitor:

And you can calculate the voltage of the capacitor if the other two quantities (Q & C) are known:

V = Q/C

Where

Q is the charge stored between the plates in Coulombs
C is the capacitance in farads
V is the potential difference between the plates in Volts

Reactance of the Capacitor:

Reactance is the opposition of capacitor to Alternating current AC which depends on its frequency and is measured in Ohm like resistance. Capacitive reactance is calculated using:

Where

X_Cis the capacitive reactance
F is the applied frequency
C is the capacitance

Quality Factor of Capacitor:

Q factor or Quality factor is the efficiency of the capacitor in terms of energy losses & it is given by:

QF = X_C/ESR

Where

X_Cis the capacitive reactance
ESR is the equivalent series resistance of the capacitor.

Dissipation Factor of Capacitor:

D factor or dissipation factor is the inverse of the Quality factor, it shows the power dissipation inside the capacitor & is given by:

DF = tan δ = ESR/X_C

Where

DF is the dissipation factor
δ is the angle between capacitive reactance victor & negative axis.
X_Cis the capacitive reactance
ESR is the equivalent series resistance of the circuit.

Energy Stored in a Capacitor:

The Energy E stored in a capacitor is given by:

E = ½ CV²

Where

E is the energy in joules
C is the capacitance in farads
V is the voltage in volts

Average Power of Capacitor

The Average power of the capacitor is given by:

P_av = CV² / 2t

where

t is the time in seconds.

Capacitor Voltage During Charge / Discharge:

When a capacitor is being charged through a resistor R, it takes upto 5 time constant or 5T to reach upto its full charge. The voltage at any specific time can by found using these charging and discharging formulas below: