Electronics
Combining resistances and conductance
Series resistances add; parallel resistances add as reciprocals. Conductance G = 1 / R turns the parallel rule into plain addition.
The Formula
R_series = R1 + R2 + ..., 1 / R_parallel = 1 / R1 + 1 / R2 + ...
Series resistances add; parallel resistances add as reciprocals. Conductance G = 1 / R turns the parallel rule into plain addition.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| R_series | Total resistance of components in a chain | ohms | 4 ohms and 12 ohms in series give 16 ohms. |
| R_parallel | Total resistance of components side by side | ohms | 4 ohms and 12 ohms in parallel give 3 ohms — smaller than either branch. |
| G | Conductance, the reciprocal of resistance | siemens | Parallel conductances simply add: G = 1 / R. |
What Each Symbol Means
R_seriesohms
Total resistance of components in a chain
4 ohms and 12 ohms in series give 16 ohms.
R_parallelohms
Total resistance of components side by side
4 ohms and 12 ohms in parallel give 3 ohms — smaller than either branch.
Gsiemens
Conductance, the reciprocal of resistance
Parallel conductances simply add: G = 1 / R.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate ohm's law page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Ohm's Law, filed under Science. Every number the guide produces comes from substituting into this one line.