Ohm's Law Made Simple

The Fundamental Formula

Ohm's Law defines the relationship between voltage, current, and resistance:

V = I × R

• V = Voltage (measured in Volts) — the electrical pressure pushing current through a circuit
• I = Current (measured in Amps) — the flow of electric charge
• R = Resistance (measured in Ohms) — opposition to current flow

The Water Pipe Analogy

Think of electricity like water flowing through a pipe. Voltage is the water pressure pushing the flow. Current is the amount of water flowing per second. Resistance is how narrow the pipe is — a smaller pipe restricts flow. Higher pressure (voltage) pushes more water (current) through the pipe, while a narrower pipe (resistance) reduces the flow.

Solving for Each Variable

You can rearrange the formula to solve for any variable:

• Find Voltage: V = I × R — multiply current by resistance
• Find Current: I = V / R — divide voltage by resistance
• Find Resistance: R = V / I — divide voltage by current

Practical Examples

Example 1: An LED requires 20mA (0.02A) of current and you have a 5V power supply. What resistor do you need? R = 5 / 0.02 = 250 Ohms. Use a standard 270-Ohm resistor.

Example 2: A 12V car battery is connected to a 4-Ohm speaker. How much current flows? I = 12 / 4 = 3 Amps.

Power formula: You can also calculate power using P = V × I, which combines with Ohm's Law to give P = I2 × R or P = V2 / R.