FirstPrinciplesa Physoly project
CIR-04circuitstrap · Sign convention error

Kirchhoff loop signs follow your traversal

  1. 01

    The tempting model

    Changing voltage signs based on how a battery or resistor looks, not on the chosen loop direction.

  2. 02

    Why it feels right

    Battery symbols seem to carry their own plus/minus direction independent of your path.

  3. 03

    Where it breaks · how to catch it

    The same element appears with different signs in two loops without a stated traversal rule.

  4. 04

    The correct model

    Pick a traversal direction. Across a resistor in the direction of current the change is −IR; across a battery from − to + the change is +ε.

  5. 05

    Repair · see it, then test it

    worked example You traverse a resistor opposite the assumed current. What voltage change do you write?

    Tempting move

    −IR because resistors always drop voltage.

    Correct move

    +IR for that traversal; the sign follows the path relative to current.

    Test the repair CIR-04 · transfer
    You traverse an ideal battery from its positive terminal to its negative terminal. What potential change enters the loop equation?

    Make a fresh prediction before referring to the worked example.