Capacitor Design Calculator

Capacitance equals charge divided by voltage

Solution

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How It Works

A capacitor stores electrical energy by holding opposite charges on two conductive plates separated by an insulator. Capacitance (C = Q/V) measures how much charge the plates hold per volt. The stored energy equation (U = ½CV²) shows that energy rises with the square of voltage, which is why high-voltage caps pack so much punch.

Example Problem

A 470 μF capacitor is charged to 25 V. How much energy does it store?

  1. Convert: C = 470 × 10−6 = 0.00047 F
  2. U = ½ × 0.00047 × 25² = ½ × 0.00047 × 625
  3. U = 0.147 J (about 147 mJ)

If the same capacitor held 0.01 coulombs of charge, the voltage would be Q/C = 0.01/0.00047 ≈ 21.3 V.

Frequently Asked Questions

What is the difference between a farad and a microfarad?

One farad is an enormous amount of capacitance. Most practical capacitors are measured in microfarads (1 μF = 10−6 F), nanofarads (10−9 F), or picofarads (10−12 F). Supercapacitors can reach several thousand farads.

How do capacitors combine in series vs parallel?

In parallel, capacitances add directly: Ctotal = C1 + C2. In series, reciprocals add: 1/Ctotal = 1/C1 + 1/C2, so the total is always less than the smallest individual capacitor.

Why does stored energy depend on voltage squared?

As voltage rises, each additional increment of charge requires more work against the growing electric field. The result is a quadratic relationship: doubling the voltage quadruples the stored energy.

What are common uses of capacitors?

Capacitors are used for power supply filtering, signal coupling, timing circuits (RC), motor starting, camera flashes, defibrillators, and power factor correction. Decoupling caps near ICs stabilize voltage and reduce electromagnetic interference.

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