Robin Barton

 
 

Basic Electrical Calculations

There are two key calculation triangles for basic electrical circuits. The first gives the relationship between voltage (V), current (I) and resistance. The second gives the relationship between power (W), voltage (V) and current (I).

!These calculations are for Ohmic conductors only.
If you are calculating for an a.c. circuit where the load is not purely
resistive see the information on power in ac circuits.

VThis shows us the following formulae:

V = IR
V╱ I = R
I = V╱R
IR

So if any two of the variables are known, the third can be calculated:

I know: I & R V & I V & R

V = A × Ω

 
WThis shows us the following formulae:

W = VI
W╱ V = I
V = W╱I
VI

So if any two of the variables are known, the third can be calculated:

I know: V & I W & V W & I

W = V × A

These can be combined giving us:

W = VIandV = IRthereforeW = (IR)I ⇒ W = I2R
 
  ⇘ R = W ╱ I2
 
  ⇘ I = ⎷W ⁄ R
 
W = VIandI = V╱RthereforeW = V * (V╱R)⇒W = V2 ╱ R
 
  ⇘ R = V2 ╱ W
 
  ⇘ V = ⎷(RW)

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