Free printable
Printable Ohm's law and power cheat sheet
A one-page Ohm's law and power cheat sheet. It puts the two triangles, the power wheel and three worked examples side by side, with the units and prefixes that trip students up at the bottom.
One page. Free to print and share for teaching. Print at actual size (100%), not fit to page. A4 suits most of the world; US Letter suits the USA and Canada.
What's on the sheet
- The Ohm's law triangle (V = I × R) and its three forms
- The power triangle (P = V × I) and its three forms
- The power wheel: all twelve formulas for P, V, I and R
- Three worked examples: a current, an LED resistor and a power rating check
- Units and prefixes: volts, amps, ohms and watts, and what M, k, m and µ do
- Check your answer: four quick sense checks, and the numbers worth knowing, like a red LED's 2.0 V
How to use it in class
Use it while students build their first circuits: they predict the current with the triangle, then measure it. The third worked example is a good discussion starter: the resistor is inside its rating, so why use a bigger one? If you allow a formula sheet in tests on Ohm's law, this one shows the method without giving away answers.
Free lesson
Now build it yourself
Each lesson comes in three short parts: see the idea, try it on a live board, then build it yourself, with quick checks as you go.
“Ohm's law” is lesson 5 of 6 in Copper Flats, Electronics World 1. Free with an account. Lessons unlock in order, so you’ll do the 4 before it first.
Or start from the very first lesson, no account neededThe charts online
Work it out
The ideas behind it
- Ohm's law explainedV = I × R: set any two of voltage, current and resistance and the third follows.
- Electrical power explained: P = V × IP = V × I: how fast energy turns into heat, and why a resistor has a power rating.
- What is voltage?The push that makes charge flow: what a volt is, and why stacked cells add up.
- What is electric current?How much charge flows past a point each second, in amps, and why it's the same all round a loop.
Questions teachers ask
What is the Ohm's law triangle?
A memory aid: V at the top, I and R side by side underneath. Cover the one you want and the other two show the sum. Cover V and you see I × R; cover I and you see V over R, so I = V ÷ R.
What is the power wheel?
A circle split into four quarters, for P, V, I and R. Each quarter holds three formulas for that quantity, so whichever two values you know, one of them works. It's Ohm's law and P = V × I combined.
Can I share the sheet with other teachers?
Yes, it's free to print, copy and share for teaching. Please keep the footer with the learnee.app link, so students can find the free lessons that go with it.
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