Electricity > Electricity Equations
Listed below are some of the most commonly used electricity equations. We can rearrange these simple equations to work out the unknown values by using the triangle method below.
Fig 1: Triangle method (Ohm's Law Triangle)
Using the triangle method, we can rearrange the Ohm's Law equation to work out the Voltage (if we know the resistance and current), the Current (if we know the voltage and resistance) or the Resistance (if we know the current and voltage).
If you place your thumb over the unknown letter, for example the R, you are left with the V over I and therefore R=V/I. Using the triangle method will help you to rearrange other three way equations.

Equation 
Written Equation 
Potential Difference (in volts) 
V = I x R 
Potential Difference (in volts) =
Current x Resistance
(can be expressed as V=IR This equation
is also known as Ohmâ€™s Law) 
Power 
P = V x I 
Voltage x Current
(can be expressed as P=VI) 
Charge 
Current x time 
Charge = Current x time
(can be expressed as Q=It) 
Energy 
E = V x Q 
Energy = Voltage x Charge
(can be expressed as E=VQ)

Total Cost 
 
Number of Units x Cost per Unit 
Electromotive force (EMF) 
E = V + Ir 
Electromotive force (EMF) =
Voltage + Current x internal resistance 
Capacitance 
C = Q / V 
Capacitance = Charge / Voltage 