Ohm's Law, on a Live Circuit
Type any two values. The circuit computes the other two and shows where each one lives.
V
A
Ω
W
Fill any two. The green ones are computed.
The two laws behind the four boxes
Ohm's law says V = I × R: push harder or lower the resistance and more current flows. The power law says P = V × I: how much of that energy turns into heat. Rearranged, they answer any question you can ask about a simple circuit, and the wheel on the Ohm's law wheel page lays out all twelve arrangements.
Reading the diagram
The battery on the left sets the voltage, the zigzag is the resistance, and the meter reads the current that results. Change the resistor and watch the current move: half the resistance, double the current, four times the power. That last one is why a resistor that felt cool at 5 V can smell interesting at 10 V.