What is Ohm’s Law?
Ohm’s Law explains the relationship between voltage, current and resistance. It is one of the first formulas used in electronics because it helps predict how a circuit behaves before it is built.
Formula
The basic formula is V = I × R, where V is voltage in volts, I is current in amperes and R is resistance in ohms. The same relationship can be rearranged to calculate current or resistance.
Example: resistor current
If a 12 V supply is connected to a 1 kΩ resistor, the current is 12 / 1000 = 0.012 A, or 12 mA.
Example: resistor power
Power can be calculated with P = V × I. In the same example, power is 12 × 0.012 = 0.144 W.
Practical design notes
Always consider resistor tolerance, power rating, temperature rise and supply variation.
Use the calculator
Try the related tool and calculate your own values instantly.
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