When Ohm's Law Breaks Down

Ohm's Law works beautifully for ohmic materials — copper wire and standard resistors, where resistance stays constant no matter the voltage. But not everything plays by those rules.

• Diodes change resistance with voltage direction — current flows one way but not the other
• Filament bulbs see their resistance jump as they heat up — roughly ten times higher when glowing than when cold

These non-ohmic devices are often more useful than plain resistors. Transistors, LEDs, and sensors all rely on this non-linear behavior to do their jobs.