Electrical Symbols and Equations

The following define the most widely used symbols and equations for capacitance (in series, parallel, quantity of stored electricity etc.), Ohm's Law (for DC circuits) and the decibel. We would also suggest you look at this 6 volume series of books by Tony R Kuphaldt 'Lessons in Electric Circuits' published under the OpenBook initiative (means its free).

Symbols used in Electrical Equations

Symbol	Meaning
C	Capacitance measured in Farads (F): Degrees Celsius (temperature)
D	Dissipation factor; reciprocal of storage factor Q.
d	Thickness of dielectric material in a capacitor (measured in centimeters)
dB	Decibel; the ratio between two amounts of Power
E	Electromotive Force measured in Volts
F	Farads (measure of Capacitance); Degrees Farenheit (temperature)
f	Frequency measured in Herz.
G	Conductance measured in siemens or mhos.
I	Current measured in amperes.
J	Energy, work or quantity of heat measured in Joules.
L	Inductance measured in henries.
M	Mutual inductance measured in henries.
P	Power measured in Watts.
Q	Quality or an inductor or Quantity of electricity stored (measured in coulombs).
R	Resistance measured in Ohms.
Z	Impedance measured in ohms.

Electrical Equations

Capacitance

In Parallel

C_total = C₁ + C₂ etc.

In Series

C_total = 1 / (1 / C₁ + 1 / C₂ etc.)

OR

1/ C_total = 1 / C₁ + 1 / C₂ etc.

Two Capacitors in series

C_total = C₁ * C₂ / C₁ + C₂

Capacitance of a Capacitor

C = 0.0885 KS (N - 1) / d

Quantity of Electricity Stored in a capacitor

Q = CE

Ohm's Law for DC Circuits

The following equations are valid for DC circuits only. Where E = volts, P = watts (power), I = current, R = resistance.

• I = E / R (current = volts / resistance)

• I = [SR] P / R (current = square root of power / resistance)

• I = P / E (current = power / volts)

• R = E / I (resistance = volts / current)

• R = P / I² (resistance = power / current squared)

• R = E² / P (resistance = volts squared / power)

• E = IR (volts = current * resistance)

• E = P / I (volts = power / current)

• E = [SR] PR (volts = square root power * resistance)

• P = I²R (power = current squared * resistance)

• P = EI (power = volts * current)

• P = E² / R (power = volts squared / resistance)

Decibel

The Decibel - a relative measure of two values is calculated for electrical circuits as:

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