Ohm's law

High School

Definition

The law stating that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written as V = IR. It is a fundamental relationship for analysing electric circuits.

Worked examples

\(V = IR \)→\( 12\,\)V\( = I \times 4\,\Omega \)→\( I = 3\,\)A\(\)

A 12-volt battery across a 4-ohm resistor pushes 3 amperes of current through the circuit.

\(V = IR \)→\( V = 0.5\,\)A\( \times 20\,\Omega = 10\,\)V\(\)

Half an amp through a 20-ohm resistor drops 10 volts across it.

\(R = \frac{V}{I} \)→\( R = \frac{9\,\)V\(}{0.03\,\)A\(} = 300\,\Omega\)

Rearrange Ohm's law to find resistance when you know voltage and current.

Common mistakes

\(V = IR \)→\( I = VR\) → \(I = \frac{V}{R}\) Current equals voltage divided by resistance, not multiplied.
Using \(V = IR\) when voltage is 12 V and power is 6 W to find current → Use \(P = VI\) first: \(I = \frac{P}{V} = 0.5\,\)A\(\) Ohm's law relates V, I, and R only — not power directly.
\(V = IR\) applies to all materials and all conditions → Ohm's law holds for ohmic conductors at constant temperature Non-ohmic devices like diodes and light bulbs don't obey a linear V = IR relationship.

Where you'll use it next

You'll use Ohm's law constantly in series and parallel circuit analysis, calculating power dissipation, designing voltage dividers, and solving Kirchhoff's laws problems in physics and engineering.

Found in 1 StudyPug lesson

Ohm's Law: The Foundation of Electrical Circuit Analysis

Physics 11

Master the fundamental relationship between voltage, current, and resistance. Learn to apply Ohm's Law in real-world circuits, from basic electronics to complex electrical systems.

11th Grade11th