What an ideal resistor looks like

In an ideal resistor, the resistance value would not change with voltage or current, nor would it change due to sudden changes in current. Real resistors cannot achieve this. Today's internal designs allow resistors to exhibit relatively small changes in resistance value under extreme voltages or currents (and even other environmental factors such as temperature).

Realistic Resistor Limits

Each resistor has an upper limit on the voltage or current it can withstand (depending on the size of the resistor). If the voltage or current exceeds this range, first the resistance value of the resistor will change (in some resistors there can be drastic changes), and then the resistor will be destroyed by overheating and so on. Most resistors will be marked with an electrical power rating, while others will provide a rated current or voltage.

In addition, the actual resistor itself has a small amount of inductance or capacitance in addition to resistance, which makes its performance different from that of an ideal resistor.