Interactive I-V graph: choose a filament bulb, diode, LED, thermistor, LDR or potentiometer, change the voltage to trace its current against voltage curve, and set the temperature, light level or knob setting to change the thermistor, LDR and potentiometer lines. A chord from the origin shows the resistance R = V/I at the chosen point and a small circuit shows charge flowing at a rate set by the current.

Ohm's law is the exception, not the rule.

A fixed resistor gives a straight I-V line, but non-ohmic devices such as bulbs, diodes, LEDs, thermistors and LDRs bend it, kink it or tilt it. Resistance is still V/I at every point; it just changes as you go. Pick a component, then change the voltage and watch its curve trace out.