Ohm's Law is the foundation of electrical engineering: V = I × R
- V (Voltage) = electrical potential difference, measured in Volts
- I (Current) = flow of charge, measured in Amperes
- R (Resistance) = opposition to current flow, measured in Ohms (Ω)
Rearranged Forms
- I = V ÷ R (find current)
- R = V ÷ I (find resistance)
Example
A 12V battery powers a 4Ω resistor. Current = 12 ÷ 4 = 3 Amps.
Power Formula
P = V × I. At 12V and 3A, power = 36 Watts.
Series vs. Parallel Circuits
In a series circuit, current is the same throughout and resistances add directly (R_total = R1 + R2 + ...). In a parallel circuit, voltage is the same across each branch and resistances combine as 1/R_total = 1/R1 + 1/R2 + ... — parallel resistance is always less than the smallest individual resistor, which surprises many students first learning circuit analysis.
Common Mistake
Ohm's Law only applies directly to purely resistive components. Circuits with capacitors or inductors under AC power require impedance (a complex-number extension of resistance) instead of simple resistance — using plain Ohm's Law on those circuits gives incorrect results.