part · Level 6 · Logic · passive
What a 10 µF capacitor does
10 µF capacitor — A tiny rechargeable bucket for charge — fills and empties to keep time.
What it is
A capacitor is two metal plates separated by an insulator. Push charge onto one plate and it attracts the opposite charge to the other, and the part holds that charge like a tiny rechargeable bucket. Capacitance says how big the bucket is, measured in farads (F); a farad is enormous, so real parts are in microfarads (µF, millionths) and nanofarads (nF, billionths).
Ten microfarads is a mid-sized bucket in this world — big enough to make visible timing with resistors in the kilohms. It comes as a small can with two legs and a stripe: this is an electrolytic capacitor and it is polarised. The leg on the stripe side is −.
Fill it through a resistor and it fills gradually; that curve is what a 555 timer, a slow-fade LED and a one-shot pulse all rely on.
How it works
Charge a capacitor through a resistor and the voltage across it rises fast at first, then slower, in a curve set by the time constant τ = R × C. After one τ it is at 63 % of the supply; after 5τ it is essentially full.
- 10 kΩ × 10 µF = 10 000 × 0.00001 = 0.1 s
- 100 kΩ × 10 µF = 1 s — a fade you can watch
- 1 MΩ × 10 µF = 10 s
The 555 uses the ⅓-to-⅔ slice of that curve, which is why its formulas carry the factor 0.693 (the natural log of 2): 0.693 × 100 kΩ × 10 µF ≈ 0.69 s per half-cycle.
How much charge? Q = C × V: at 4.5 V a 10 µF cap holds 45 microcoulombs. Dumped through an LED that is a brief flash, not a hazard — at this voltage capacitors are harmless.
The numbers
| Capacitance | 10 µF — tolerance often ±20 % |
|---|---|
| Polarity | stripe = −, long leg = + — electrolytic — never reverse it |
| Voltage rating | typically 16–50 V — any rating above 4.5 V is fine |
| τ with 100 kΩ | 1 s — R × C |
| Charge at 4.5 V | 45 µC — Q = C × V |
See it working
The 555 blinker from the library, simulated live. Open it on the Workbench to change anything.
simulating…
Mistakes everyone makes
- In backwards. An electrolytic run in reverse heats, swells and can pop its vent. Fix: stripe to −; the longer leg is +.
- Blink timing far off. The label is ±20 % and it drifts with age. Fix: expect it; use a film capacitor when timing matters.
- Reading the code wrong. Small caps say "104" (10 × 10⁴ pF = 100 nF); this one says "10µF" or "10uF" plainly.
- Legs bridging rows. Short legs on a can-type cap slip into neighbouring breadboard rows. Fix: check it sits across the rows you meant.
Questions people ask
- What does a 10 µF capacitor do in a 555 circuit?
- It is the timing capacitor. It charges through R1 and R2 and discharges through R2, and the 555 flips its output each time the capacitor voltage crosses ⅓ or ⅔ of the supply.
- Which side of an electrolytic capacitor is negative?
- The side with the stripe (often with − signs printed on it). The longer leg is positive.
- How long does a capacitor take to charge?
- About 5 × R × C to be practically full. Through 100 kΩ a 10 µF capacitor reaches 63 % in 1 second and is full in about 5.
Projects that use this part
No project uses it yet — it arrives at Level 6, and the projects for that level are still being written and verified.
verified against: SparkFun — Capacitors · Kuphaldt — Lessons in Electric Circuits, Capacitors