Ohmy

A daily circuit puzzle. Find every volt, amp, and ohm.

Today

Practice

Resistor Rush

Read or build as many resistors as you can in 60 seconds.

Some show you the color bands: type the value and press Enter. Others give you the value: tap the colors, then press Enter. When there's a tolerance, pick it too.

Stuck? Hold Peek to see the numbers behind the colors, or slide it right to keep them showing. You can also open the chart. A resistor you peek at doesn't score, except in practice.

On a keyboard: type values with k and M, press 0 to 9 for a color, G for gold, S for silver, and Enter to answer.

SymbolsSchematic symbols

Tap a symbol to study it. Rate how well you know each one; the quiz asks more about the ones you don't know yet.

How to play

Fill in every empty box. Each card is one part of the circuit, with its voltage (V), current (A), and resistance (Ω). Every puzzle can be solved by logic alone.

Ohm's law

V = I × R

V is voltage in volts (V), I is current in amps (A), and R is resistance in ohms (Ω).

Works on every card, and on any group of cards. Here, 12 ÷ 2 = 6 Ω.

Series: one path

The current is the same through each part. Voltages add: 4 + 8 = 12 V. Resistances add: 2 + 4 = 6 Ω.

Parallel: side by side

Every branch gets the same voltage. Currents add: 1 + 2 = 3 A. Resistance: 1 ÷ (1/6 + 1/3) = 2 Ω.

Resistor color code

The first two bands are digits and the third is the multiplier. Gold multiplies by 0.1 and silver by 0.01. The last, separate gold band is tolerance, so skip it. Yellow, violet, gold is 47 × 0.1 = 4.7 Ω.

Turn on Color-code resistances in Settings to practice reading them.

The battery card holds the whole circuit's totals: its voltage, total current, and total resistance.

Tools

Clear
Empties the selected box or note, or the calculator. ⌫ deletes one digit. To see wrong values as you go, turn on Show mistakes right away in Settings.
Calc
Tap ×, ÷, +, −, or 1/x (parallel resistance) above the keypad to calculate; it lights up blue, and so do the number keys. Tap values to drop them in, and keep tapping to add more. Tap the answer to place it. If every value came from one card, it fills that card's empty box. Otherwise it becomes a note. Or tap any empty box to drop the answer straight into it, or tap open space to drop it into a new note there. Once you use an answer, the calculator clears. If you pick another operation before using it, the answer becomes that operation's first value; anything else you'd entered clears. Tap the lit operation again to turn the calculator off and clear it, and Clear to start over.
Notes
Tap any empty spot to jot down a value, like a combined resistance. Tag it V, A, or Ω, or delete it. Drag the top strip to move a note, or drag its number to copy it into a box or the calculator.
Zoom
Pinch the circuit with two fingers to zoom in or out, and swipe to look around. On a laptop, pinch the trackpad.
Drag
Drag any value onto a box or a calculator slot to copy it there.
Meter
Measures one box for you. You get 3 per puzzle.
Groups
In Hard puzzles, tap Group, tap two or more resistors, then tap Group again to group them. The group gets a dashed outline and its own card for its voltage, current, and combined resistance. Group boxes are for your working: they aren't checked, and you don't need them to win. Tap × on the card to remove a group.

Puzzles

Easy uses whole numbers, Medium one decimal place, and Hard two. Classic gives you the battery voltage and every resistance. Mixed gives you any mix of values. Meter puzzles start with too few clues, so you measure the fewest boxes you can and try to match par.

Color chart

ColorDigitMultiplierTolerance

Read bands from the end they crowd toward. The tolerance band sits apart. No tolerance band means ±20%.

Settings

Circuit complete

Think a friend can solve it? Send them this exact circuit.