Ohm's Law: Predicting Current in Series and Parallel Circuits

Hi, I'm Lumi. Let's figure out what controls current in a circuit. A battery maintains a fixed voltage (V) — think of it as the pressure pushing charges around the loop. The wires and components resist that flow; we call that resistance (R), measured in ohms (Ω). The resulting flow of charge is current (I), measured in amperes (A). Ohm's law ties all three together: V = I × R Rearrange it when you need a different quantity: I = V ÷ R, or R = V ÷ I. For example, 12 V across 4 Ω gives I = 12 ÷ 4 = 3 A. If you ever feel stuck, write the equation first, label what you know, and the unknown falls out. In a SERIES circuit, all components share one single loop. The same current passes through every part, and the individual resistances add together into one total: R_total = R1 + R2 + … . Because R_total is larger, Ohm's law tells us current must be smaller for the same voltage. Adding a series resistor always reduces total current. In a PARALLEL circuit, components sit on separate branches that share the same two connection points. Each branch sees the full battery voltage independently. The branch currents add together to give total current leaving the battery. Adding a parallel branch opens a new road for charge, which lowers total resistance and raises total current. One conservation rule ties everything together: charge is never created or destroyed. At any junction, the total current flowing in must equal the total current flowing out. This is why, in the activity below, you can find an unknown branch current by subtraction.