Enter any two known values to instantly calculate the missing one — Voltage (V), Current (I), Resistance (R), or Power (P).
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Ohm's Law is one of the most fundamental principles in electronics and electrical engineering. It states that the voltage across a conductor is directly proportional to the current flowing through it, with the proportionality constant being the resistance. Named after German physicist Georg Simon Ohm, who published it in 1827, the law is expressed as:
Where V is voltage in Volts (V), I is current in Amperes (A), and R is resistance in Ohms (Ω).
| Quantity | Symbol | Unit | Description |
|---|---|---|---|
| Voltage | V | Volt (V) | Electrical potential difference — the "pressure" pushing current |
| Current | I | Ampere (A) | Rate of electric charge flow through a conductor |
| Resistance | R | Ohm (Ω) | Opposition to current flow in a material |
| Power | P | Watt (W) | Rate of energy consumption or generation |
| Solve for | Formula 1 | Formula 2 | Formula 3 |
|---|---|---|---|
| Voltage (V) | V = I × R | V = P ÷ I | V = √(P × R) |
| Current (I) | I = V ÷ R | I = P ÷ V | I = √(P ÷ R) |
| Resistance (R) | R = V ÷ I | R = V² ÷ P | R = P ÷ I² |
| Power (P) | P = V × I | P = I² × R | P = V² ÷ R |
Voltage (V) is the electrical potential difference between two points — it's the "pressure" that drives electric current through a circuit. A 9V battery has 9 volts of potential difference between its positive and negative terminals.
Current (I) is the flow of electric charge through a conductor, measured in Amperes (amps). 1 amp = 1 coulomb of charge passing a point per second. A typical LED uses about 20 milliamps (0.02A), while a household appliance might draw 10–15 amps.
Resistance (R) is a material's opposition to the flow of electric current, measured in Ohms (Ω). Materials with low resistance (like copper) are good conductors. Materials with high resistance (like rubber) are insulators. Resistors are components used to control current in circuits.
Electrical power (P) is the rate at which electrical energy is consumed or generated, measured in Watts (W). A 60W light bulb consumes 60 joules of energy per second. Power = Voltage × Current (P = V × I).
Suppose you have a 12V car battery and a 6Ω resistor. Using Ohm's Law: I = V ÷ R = 12 ÷ 6 = 2A. The current flowing through the resistor is 2 amps. The power dissipated is P = V × I = 12 × 2 = 24 watts.
No — Ohm's Law only applies to ohmic (linear) conductors like resistors where resistance stays constant regardless of voltage or current. Non-ohmic components like diodes, transistors, and LEDs have a non-linear relationship between voltage and current and don't follow Ohm's Law strictly.
The Ohm's Law wheel (or Ohm's Law triangle) is a visual reference tool showing all 12 formulas relating V, I, R, and P in a circular diagram. It's widely used by electricians and electronics students to quickly look up which formula to use.