What does a capacitor actually do?
A capacitor stores energy in an electric field. It charges when a voltage source moves charge onto its plates and releases stored energy when connected to a suitable load. Its voltage cannot change instantaneously in an ideal circuit.
By the end, you can…
- Explain capacitance, voltage rating, polarity, and common capacitor types.
- Predict charge/discharge voltage, current, time constant, and stored energy.
- Combine capacitors in series and parallel and explain practical limitations.
- Recognize plausible symptoms of open, shorted, and leaky capacitors.
- Interpret basic measurements and choose the next diagnostic test.
Safety: All activities here use a simulated low-voltage circuit. Real capacitors—including automotive high-voltage systems and airbag reserve-energy circuits—can retain hazardous energy after power is disconnected. Follow manufacturer service information and qualified-person procedures; do not probe or discharge such systems as a practice exercise.
10 lessons: from concept to technician
Open each lesson. Use the interactive labs to test what you learn instead of memorizing a formula alone.
RC Charge & Discharge Workbench
Adjust the supply, resistance, and capacitance. Then charge or discharge the capacitor. The graph models an ideal series RC circuit; actual components have leakage, tolerance, and other non-ideal behavior.
Voltage against elapsed time
Capacitor bank builder
Choose two ideal capacitors and connect them in parallel or in series. Watch how equivalent capacitance and stored energy change at the chosen applied voltage.
Important: This builder assumes ideal, initially uncharged capacitors. Real series capacitor banks may not divide voltage equally because of leakage and tolerance. Never assume a series connection automatically makes any arbitrary capacitor bank safe at a higher voltage.
Virtual multimeter lab
Choose a simulated component condition, meter mode, and connection. Your goal is to distinguish an observation from a diagnosis.
Automotive diagnostic decisions
Three simulated cases. Select the next action supported by the evidence; more than one real-world fault may create similar symptoms.
Earn your completion badge
Answer all five questions. A score of 4/5 or higher completes the quiz. You can review and try again.
Capacitors: Store the Charge. Control the Change.
Complete the seven learning sections and pass the knowledge check to unlock your badge.