Ohm's Law formula:
story, analogy and memory trick
The Ohm's Law formula is V = I × R. The current through a conductor is directly proportional to the voltage across it, as long as its resistance and temperature stay constant.
The Ohm's Law formula
- Vvoltage across the conductor, in volts
- Icurrent, in amperes
- Rresistance, in ohms
The story
Imagine a water tank on a hill. The height of the tank is the voltage V, the push that sends water down a pipe. A thin, rough pipe is the resistance R and slows the flow. The water that leaves each second is the current I. Raise the tank and more water flows. Make the pipe thinner and less flows.
Real-life analogy
Think of traffic on a road. The push from the junction is V, a narrow lane full of potholes is R, and the number of vehicles that get through each minute is I.
Memory trick
Draw a triangle with V on top and I and R at the bottom. Cover the letter you want: V = I × R, I = V ÷ R, R = V ÷ I.
Exam tip
Ohm's law applies to ohmic conductors at constant temperature. On a graph of V against I, the slope equals R.
Questions about Ohm's Law
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More Physics formulas
Newton's Second Law
F = m × a
The net force on an object equals its mass multiplied by its acceleration, so the same push speeds up a lighter object more than a heavier one.
Read the storyKinetic Energy
KE = ½ × m × v²
The kinetic energy of a moving object is half its mass times the square of its speed, so speed matters far more than mass.
Read the storyFirst Equation of Motion
v = u + at
The final velocity equals the initial velocity plus the acceleration multiplied by the time, for straight-line motion with constant acceleration.
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