FirstPrinciplesa Physoly project
CIR-07circuitstrap · Circuit equivalence error

A charged capacitor blocks steady DC

  1. 01

    The tempting model

    Treating a capacitor as a wire after a long time in a DC circuit.

  2. 02

    Why it feels right

    At first current flows while charge moves, so it seems the path remains conducting.

  3. 03

    Where it breaks · how to catch it

    You assign a nonzero steady current through a capacitor in a DC circuit.

  4. 04

    The correct model

    After a long time, an ideal capacitor in DC is fully charged and no current flows through its branch. Initially it can act like a short; at steady state it acts like an open circuit.

  5. 05

    Repair · see it, then test it

    worked example A capacitor and resistor are connected to a battery for a long time. What is capacitor current?

    Tempting move

    V/R forever.

    Correct move

    Zero at steady state.

    Test the repair CIR-07 · transfer
    An initially uncharged capacitor is connected in series with a resistor to an ideal battery. Immediately after closing the switch, the current is:

    Make a fresh prediction before referring to the worked example.