I passed small voltages (0-5V) through a known resistance, measured the current each time, and got different "effective resistances" for each case. However, when graphed, the effective resistances appear to approach the known resistance of the circuit as a limit at higher voltages. What is the reason for this? Nobody I ask can give me a satisfactory response. I've been told resistance never changes .... is it due to the inner workings of the ammeter I'm measuring it with? Thanks!