Worksheet 0 - Ohm's Law

Here is WS0 (pdf).

Kirchhoff's Node law:
At any point in a circuit, $$\sum I_\text{in}= \sum I_\text{out}$$

• Dead ends: No current in or out on the right means no current out or in on the left. (Unless an explicit current is given...)
  
• Choose a direction:
  E.g. Maybe you know the directions of $I_1$ and $I_2$, but are unsure about $I_3$
  
  Just pick a direction. Later on, you might solve for $I_3$: If you find that it's negative then your initial guess was wrong, but now you *know* which way it's going.