DC Circuits

The linear relationship between voltage, current, and resistance — the foundation of every DC circuit.

P = VI in three algebraic forms, energy accounting in DC resistor circuits.

Single-loop circuits, common current, summing voltages and resistances.

Common voltage, reciprocal resistance addition, branch current distribution.

Reducing mixed networks step-by-step to find totals and branch quantities.

Algebraic sum of voltages around any closed loop equals zero. The loop-level energy-conservation law.

Algebraic sum of currents at any node equals zero. The node-level charge-conservation law.

The series-circuit formula that picks off a fraction of the source voltage.

How parallel branches split the source current by conductance.

Real batteries: source EMF, internal resistance, terminal voltage under load.