What a learner can do afterwards
- States Ohm's Law as V = IR and identifies the units for each quantity
- Rearranges V = IR to find the unknown value given the other two
- Explains that resistance opposes current flow and identifies factors that affect resistance (material, length, thickness)
The lesson
You already know that voltage pushes charge through a circuit, and current is how much charge flows past a point each second. Resistance is the third piece. It measures how much a circuit fights against that flow. Ohm's Law ties all three together: V = I x R. Voltage (V) is measured in volts, current (I) is measured in amps, and resistance (R) is measured in ohms, written with the symbol Ω.
A circuit has a 12-volt battery and a 4-ohm resistor. To find the current, rearrange the formula: I = V divided by R. Divide 12 by 4, and the current is 3 amps.
Think of resistance as friction for electric charge. A thick, short wire has low resistance, so current flows easily. A thin, long wire, or one made from a material like rubber instead of copper, has high resistance and fights the flow much more.
V = I x R. Know any two of voltage, current, or resistance, and the formula gives you the third.
Watch it
Where it sits
Learn first
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.