# Why is current and not voltage varied for a Superconductor?

I am an undergraduate physics student and recently undertook an experiment in which the resistance of a superconductor, and a semiconductor, was investigated at different temperatures. The resistance was obtained from V/I measurements and for the semiconductor the voltage was varied and the current recorded, but for the superconductor it was the current that was varied.

My understanding is that the voltage or current could have been varied for the semiconductor, and was simply done this way to easily obtain the characteristic V-I curve, however I don't understand why we were specifically instructed to only vary the current for the superconductor. What is the physical reason behind this?

• Because resistance of a super conductor (up to certain current densities) is 0, no voltage can exist between one and the other end of the superconductor. Apr 17, 2018 at 8:32

Since the resistance is almost equal to $R\approx0$ in a superconductor and $I=\frac{V}{R}$ you will most likely be able to measure a really high current, when compared to the semi-conductor. Could be that he wants you to notice this big difference, not really sure tho:) Hope it helps