Can capacitors store an electrical charge even when they are disconnected from a power source?

• A. True
• B. False
• C. They store a charge only when connected to a source
• D. Only after a period of time

Answer: (A)

Yes. A capacitor can store charge even after the power source is removed. When it’s charged, one plate takes on excess electrons and the other has a deficit, creating an electric field between the plates. This separation of charge represents stored energy in the electric field.

Once the charging source is disconnected, there’s no complete path for current to flow, so the charges can’t recombine and the voltage across the plates remains for a time. In an ideal capacitor with perfect insulation, this charge would stay indefinitely. Real capacitors, however, have some leakage through the dielectric and other small paths, so the charge slowly leaks away and the voltage decays over time. The rate of decay is characterized by the leakage resistance and the capacitor’s value, often described by the time constant τ = R_leak × C.

In practical terms, a capacitor can hold a charge long enough to be measured or used in a circuit after power is removed, until it’s discharged through a load or leakage path.