Series Circuits
One current path passes through every series component, so current is the same through each resistor. Voltage drops add to the source voltage.
Rtotal = R1 + R2 + ...
Parallel Circuits
Each branch connects across the same two nodes, so branch voltage is equal. Branch currents add to total current.
1/Rtotal = 1/R1 + 1/R2 + ...
For two resistors: Rtotal = R1R2 / (R1 + R2).
Quick Checks
- Series resistance is greater than either individual resistor.
- Parallel resistance is lower than the smallest branch resistance.
- Opening a series path stops all current.
- Opening one parallel branch does not necessarily stop other branches.
Power Distribution
In series, the larger resistance dissipates more power for the same current. In parallel, the lower resistance draws more current and dissipates more power at the same voltage.
Every component must be checked for its own voltage, current, and power rating.