Ohm's law
Calculate voltage, current, or resistance for an ohmic component using compatible electrical units.
U = I × R Calculated quantities
U - voltage · I - electric current · R - resistance
Physics formulas
Electricity and circuits
Calculate voltage, current, resistance, power, and other quantities used to analyse electric circuits.
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How to choose the right formula
Ohm's law
U = I × R - When to use it
- For an ohmic component under stable physical conditions, voltage equals current multiplied by resistance.
- Calculated quantities
- U - voltage (V) · I - electric current (A) · R - resistance (Ω)
- Worked example: Current through a resistor
- A 6 Ω resistor has 12 V across it. Calculate the current.
What to check before calculating
Assumptions and conditions
- The component is ohmic over the considered operating range.
- Physical conditions that affect resistance, especially temperature, are treated as constant.
- Resistance used as a divisor must be greater than zero.
- Current used to calculate resistance must be non-zero, and all prefixes must be converted consistently.
Common mistakes
- Applying Ohm law to a non-ohmic component without checking its current-voltage behaviour.
- Mixing milliamperes with amperes or kilohms with ohms.
- Dividing resistance by voltage instead of voltage by resistance when finding current.
- Assuming resistance is constant while the component temperature changes substantially.