Physics
Ohm's Law
Ohm's law is V = IR — voltage equals current times resistance. Together with Kirchhoff's laws, it lets you analyze almost any DC circuit.
How to Approach Ohm's Law
Identify the circuit type
Series (single path), parallel (multiple paths), or combined. The way resistors combine depends on this.
Reduce resistances
Series: R_total = R₁ + R₂ + ... Parallel: 1/R_total = 1/R₁ + 1/R₂ + ... Keep reducing until you have one equivalent resistance.
Apply V = IR
Use Ohm's law on the equivalent circuit to find total current. Then work backwards through your reductions to find current and voltage at each component.
Frequently Asked Questions
What units does each variable use?+
Voltage V is in volts (V). Current I is in amperes (A). Resistance R is in ohms (Ω). Always work in SI units before plugging in.
Does Ohm's law work for AC circuits?+
Yes, but with complex impedance Z replacing R: V = IZ. For pure resistors, Z = R and you're back to Ohm's law.
What if resistance changes with temperature?+
Ohm's law still holds at any given temperature. Most metals get more resistive as they heat up — semiconductors do the opposite.
Related Topics
More step-by-step guides in Physics and adjacent subjects.
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