FirstPrinciplesa Physoly project
CIR-08circuitstrap · Circuit equivalence error

Changing equivalent resistance changes the source current

  1. 01

    The tempting model

    Adding a parallel branch but keeping total current fixed.

  2. 02

    Why it feels right

    The battery voltage is fixed, so the current can feel fixed too.

  3. 03

    Where it breaks · how to catch it

    You add a resistor in parallel and do not update current drawn from the battery.

  4. 04

    The correct model

    For an ideal voltage source, I_total = V/R_eq. Adding a parallel branch lowers R_eq, so total source current increases.

  5. 05

    Repair · see it, then test it

    worked example A second identical bulb is added in parallel to one bulb on a battery. What happens to total current?

    Tempting move

    It stays the same and splits.

    Correct move

    It doubles for ideal identical bulbs; each branch still gets battery voltage.

    Test the repair CIR-08 · transfer
    A resistor is added in parallel across an ideal voltage source. What happens to total source current?

    Make a fresh prediction before referring to the worked example.