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📐 Ohm's Law

Master the equation at the heart of electronics, V = I × R, and learn to rearrange it to find voltage, current, or resistance in any simple circuit.

lessons

~15 min

to learn

🔬 Science

subject

Teens

level

Start the course →

What you’ll learn

The RelationshipIdentify voltage, current, and resistance and describe how they depend on one another.Every simple circuit involves voltage (the push, in volts), current (the flow, in amps), and resistance (the opposition, in ohms). For a fixed resistance, more voltage means more current; for a fixed voltage, more resistance means less current. Georg Ohm discovered the pattern linking them in the 1820s.
Ohm's Law V=IRState Ohm's law as V = I × R and recognise its straight-line current-voltage graph.Ohm's law states that voltage equals current multiplied by resistance: V = I × R. For a component that obeys the law, current is directly proportional to voltage, giving a straight line through the origin on a current-voltage graph. Knowing any two quantities lets you find the third.
Using Ohm's LawRearrange and apply Ohm's law to find voltage, current, or resistance, and know its limits.Ohm's law can be rearranged to I = V ÷ R or R = V ÷ I to find whichever quantity is unknown. For example, 12 V across 4 Ω gives 3 A. The law holds for ohmic components like fixed resistors, but not for non-ohmic ones like filament bulbs, whose resistance changes as they heat up.

Questions this course answers

For a fixed resistance, what happens to the current when the voltage rises?

With resistance fixed, a higher voltage drives a larger current.

What is Ohm's law?

Ohm's law states that voltage equals current multiplied by resistance: V = I × R.

What does a graph of current against voltage look like for an ohmic resistor?

For an ohmic resistor, current is proportional to voltage, giving a straight line through the origin.

A 12 V supply is connected across a 4 Ω resistor. What is the current?

Using I = V ÷ R, the current is 12 ÷ 4 = 3 amps.

If you know the voltage and current, how do you find the resistance?

Rearranging Ohm's law gives R = V ÷ I: divide voltage by current to find resistance.

Why is a filament bulb described as non-ohmic?

As current rises the filament heats up and its resistance changes, so it does not obey Ohm's law.

Grounded in trusted sources

BBC Bitesize
The Physics Classroom
HyperPhysics

Every Wunder lesson is built from real, reputable sources — never invented.

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