Circuits Part 2: Kirchhoff's Rules & Power

Kirchhoff's Rules

The junction rule conserves charge (current in = current out); the loop rule conserves energy (gains = drops around any loop). Collapse a network from the inside out, then walk back out for branch values. A series divider shares voltage in proportion to resistance; a parallel divider sends more current down the smaller resistance.

Power

$P = IV = I^2R = \frac{V^2}{R}$ In series the larger resistor dissipates more; in parallel the smaller one does. Brightness is power. Current, not voltage, does the harm in a shock.

Key Takeaways

• Charge and energy are conserved at every junction and around every loop.
• Pick the power form that holds the known quantity constant.
• Adding a parallel branch lowers total resistance and raises total current.