1. Kirchhoff’s Rules

2. Kirchhoff’s Current Law (1)
KCL: The sum of currents entering any junction in a circuit must equal sum of currents leaving that junction.

3. Kirchhoff’s Current Law (2)
KCL: The sum of currents leaving any junction in a circuit must be zero
+ If Ii leaves
- if Ii enters

4. Kirchhoff Voltage Law (1)

5. Kirchhoff Voltage Law (2)
KVL: Sum of potential differences across all elements around any closed circuit loop must be zero.
+ If in the sense of the loop
- if against the sense of the loop

6. Voltage drop between two points
The voltage drop between two points is the sum of voltage drops across each element.
+ If in the sense of the path a  b
- if against the sense of the path ab

7. Steps of Solving a Circuit Problem
1. Straighten out circuit (make squares)
2. Simplify resistors in series/parallel
3. Assign currents, simplify with KCL
4. Write KVL (1 per loop)
5. Solve

8. Example: Simple Circuit
You can simplify resistors in series (but don’t need to)
What is current through the bottom battery?