Ohm’s Law Explained: Voltage, Current and Resistance

Understand volts, amps and ohms through practical relationships rather than memorizing numbers without context.

Key formula

I = V ÷ R · V = I × R · R = V ÷ I

Worked example: 12 V ÷ 100 Ω = 0.12 A = 120 mA

What is Ohm’s law?

For many resistive circuits, current increases when voltage rises and decreases when resistance rises. Ohm’s law describes this relationship.

Voltage (V) is electric potential difference, current (I) is measured in amperes, and resistance (R) is measured in ohms. Ohm’s law models ohmic components; it does not fully describe every electronic device.

Three useful formulas

Given voltage and resistance, divide voltage by resistance to find current. Rearrange the same equation to solve for the other values.

Step-by-step example

Imagine a 12 V source connected to a 100 Ω resistor. Identify the quantities: voltage = 12 V and resistance = 100 Ω. Divide 12 by 100 to obtain 0.12 A, or 120 mA.

To estimate resistor power, multiply voltage by current: 12 V × 0.12 A = 1.44 W. A real circuit needs a resistor with an appropriate power rating and safety margin; low-wattage resistors can overheat.

Common mistakes

Do not mix up milliamps and amps: 1000 mA equals 1 A.

Do not connect an LED directly to 12 V assuming it behaves like a fixed resistor.

Avoid practicing on mains electricity. Use safe low-voltage learning circuits or simulations.

Try the Ohm’s law calculator ↗

Educational content: verify the conditions of your real situation before relying on the result.