Science calculator

Capacitor energy and RC time.

Solve the energy stored by a capacitor or the time constant of an ideal RC circuit. Enter two values and leave one blank.

Relationship

Stored energy E

Capacitance C

Potential difference V

Stored energy ESolved

—

E = ½CV²

Charge magnitude Q = CV: —

Display precision

E = \frac{1}{2} C V^{2}

τ = R C

E stored energy · C capacitance · V potential difference · τ time constant · R resistance

Assumptions

Ideal capacitor with constant capacitance and no leakage, dielectric loss or breakdown.
V is the potential-difference magnitude across the capacitor; stored energy cannot be negative.
The RC relationship describes a first-order circuit with one effective resistance and one capacitance.
After one time constant, charging has reached about 63.2% of its final change; discharging has about 36.8% remaining.

How it works

A capacitor stores separated charge. Raising its potential difference requires progressively more work, giving the factor one half in E = ½CV².

The RC time constant sets the pace of exponential charging and discharging. A larger resistance limits current and a larger capacitance requires more charge, so either one increases τ.

Choose a relationship and leave its unknown field blank. The answer is a component or circuit value, not a component safety or energy-rating recommendation.

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