KIRCHHOFF’S CIRCUIT LAWS

•Voltage Rule

•Current Rule

KIRCHHOFF’S CIRCUIT LAWS

1. Voltage Rule. This is based on the conservation of

energy: “the sum of voltages around a closed conducting loop (that is, a circuit) must be zero”

Supplies energy (or work)

Voltage+

ResistanceUses energy (does work)

KIRCHHOFF’S CIRCUIT LAWS

In other words, the net work done must be zero.

Net Work = 0

NOTE: The Resistor can’t do more work than is available…and it can’t do less!(if there’s too much energy generated, it burns out)

KIRCHHOFF’S CIRCUIT LAWS

2. Current Rule.This is based on the conservation of charge:“the sum of currents entering a junction = the sum leaving”1

1[a junction is a place where 2 or more conductors join]

Resistor R1

I

I2I1

KIRCHHOFF’S CIRCUIT LAWS

So we see that

I = I1 + I2

This relationship is the essence of the Current Rule