Circuit Builder — Ohm's Law Simulator

The fundamental law governing resistors, defining the linear relationship between voltage, current, and resistance.

V = Voltage (Volts, V) — The electrical "push" or potential difference.
I = Current (Amperes, A) — The rate of flow of electric charge.
R = Resistance (Ohms, Ω) — The opposition to current flow.

For circuits with multiple resistors, the total resistance depends on their configuration. Power dissipation (heat) in a resistor is also critical.

$R_t$ = Total equivalent resistance.
P = Power (Watts, W) — The rate of energy conversion to heat.
The power equations show that for a fixed resistance, doubling the voltage quadruples the power (and heat) dissipated.

Electronics Design: Every circuit board uses these principles. Engineers calculate resistor values using Ohm's Law to ensure components like LEDs get the correct current (e.g., a 2V LED with a 5V supply needs a series resistor to limit current and prevent burnout).

Household Wiring & Safety: Home circuits are designed with specific voltage (120V/240V) and wire resistance to limit current. Fuses and circuit breakers are rated using $P = I^2R$ heating calculations—they trip when current (and thus heat) exceeds a safe level for the wiring.

Sensor Interfaces: Many sensors (like temperature-sensitive thermistors) change resistance. By placing them in a voltage divider circuit (two resistors in series), Ohm's Law lets you convert the measured voltage into a precise resistance value, which can then be translated into a temperature reading.

Power Supply Regulation: Voltage regulators and power adapters use resistor networks to sample the output voltage. If it drifts, a feedback circuit adjusts to maintain a steady voltage, ensuring your laptop or phone charges correctly and safely.

Here are a few points beginners often stumble on when starting with the simulator. First is the image that "current flows from high voltage to low voltage". This is mostly correct, but the story changes with AC circuits or when capacitors and coils are involved. Try lowering the power supply voltage to zero in this tool's RC circuit mode. If the capacitor is charged, current will flow from the capacitor towards the resistor (discharge), right? The direction of current is determined by the potential difference, so it doesn't always flow only from the power supply's positive terminal.

The second point is the realism of parameter settings. For example, setting the power supply voltage to 100V and the resistance to 0.1Ω results in a calculated current of 1000A according to Ohm's law—an outrageous value. While the simulation can calculate it, in reality, neither batteries nor wires could handle such a large current and would risk catching fire. In practice, you should always be mindful of the ratings (allowable power, allowable current) of the components you use. For instance, connecting 5V across a 100Ω, 1/4W resistor gives a current of 0.05A and a power consumption of $P=I^2R = 0.05^2 \times 100 = 0.25W$, which is barely safe. But if you change the resistance to 10Ω, the power consumption becomes 2.5W and it will smoke in an instant.

The third point is understanding that "ground (GND) is just a reference point". In the simulator, think about what point the voltmeter is using as a reference. Often, voltage is the potential difference between two points. For example, in a voltage divider circuit, even if the output point voltage is displayed as "2.5V", that value is relative to GND (0V). If you measure using a different point as a reference instead of GND, the displayed voltage value would be completely different. When drawing a schematic, deciding where to place GND is an important design choice to simplify calculations.