Turtleand Energy

Rung 5 · See change over time

Watch an RC circuit remember

Charge and discharge a capacitor through a resistor while following voltage and current over time.

foundation30 minutes0 of 4 stages explored
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A switch selects five volts or ground, feeding a ten kiloohm resistor and one hundred microfarad capacitor.
5 V or ground selected by a switch -> 10 kiloohm resistor -> 100 microfarad capacitor -> ground

Knowledge this exercise builds on

Lesson 5: DC vs ACLesson 7: Power and Energy: Watts, Watt-hours, and Electric Bills

Practice loop

Try each step before revealing its answer.

The task stays visible. Revealing a numbered answer remembers that stage as explored in this browser. It is not a grade.

ComponentsSee the parts and values before you start.
  • One 5 V DC voltage source
  • One two-position switch
  • One 10 kΩ resistor
  • One 100 µF capacitor
  • Two scopes, for capacitor voltage and resistor current
PredictCommit to an expected result before running the circuit.

Predict whether capacitor voltage and current jump instantly when charging begins. Calculate the time constant with:

τ = R × C
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The time constant is:

τ = 10,000 Ω × 0.0001 F = 1 second

Capacitor voltage cannot jump instantly. Charging current can jump to 5 V / 10 kΩ = 0.5 mA, then falls as the capacitor charges.

BuildWire the circuit yourself from a blank canvas.

Use the switch to connect the resistor either to 5 V for charging or to ground for discharging. Keep the capacitor connected to ground.

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The resistor and capacitor stay in series, with the capacitor bottom connected to ground. The two-position switch should connect the resistor top to 5 V for charging or to ground for discharging.

MeasureSee what to inspect, compare, and change.

Record capacitor voltage and resistor current at the start, after 1 second, and after several seconds. Switch to discharge and compare the shape and direction of the two traces.

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After one time constant, capacitor voltage reaches about 63 percent of 5 V:

V₍C₎ ≈ 3.15 V after 1 second

Current starts near 0.5 mA and falls toward zero. During discharge, capacitor voltage decays smoothly and current reverses direction before also falling toward zero.

ExplainConnect the observation back to your model.

Explain what the capacitor stores, why the resistor limits the initial current, and why the waveform changes fastest at the beginning.

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The capacitor stores energy in an electric field and resists an instantaneous voltage change. The resistor limits current. The voltage difference across the resistor is largest at the beginning, so current and capacitor voltage change fastest then. Together, resistance and capacitance set the response time.

Optional referenceReveal reference circuitCompare only after you build. Opening this panel does not contact Falstad.

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Safety boundary

This is a low-voltage educational model.

Do not translate it into mains construction, household wiring, battery-pack work, or real protection settings. Real electrical systems need rated components, proper protection, test equipment, and qualified safety judgment.