Ohm's Law and DC Circuits
Ohm's law relates voltage, current, and resistance: V = IR. It is the foundation for analyzing simple and combined resistor circuits.
Voltage, current, and resistance
Current is the rate of charge flow. Resistance opposes that flow. For an ohmic resistor, doubling the voltage doubles the current.
Series and parallel combinations
Resistors in series add directly. In parallel, the reciprocal of the equivalent resistance equals the sum of reciprocals of each branch.
Measure it interactively
Build circuits in the Circuits lab, attach meters, and verify Ohm's law with live readings as you change resistance or battery voltage.
Ohm's Law
In a circuit, voltage is the electrical push and current is the flow of charge it produces. Ohm's law says the current through a resistor is proportional to the voltage across it — and the resistance tells you how strongly the resistor opposes that flow.
V = I · R
- V — voltage (V): the electrical push across the component
- I — current (A): the flow of electric charge through the component
- R — resistance (Ω): how strongly the component opposes the current
A 9 V battery is connected across a 3 Ω resistor. How much current flows?
- V = 9 V
- R = 3 Ω
- I = V / R
- I = 9 V / 3 Ω
I = 3 A