I have trouble understanding how the following experiment tests Ohm's Law. Imagine a simple DC circuit with a 6V battery connected to a resistance that is in parallel with a voltmeter and in series with an ammeter. Switch on the circuit, and measure the resistance, voltage and current. Plot that as a point on a voltage (y axis) vs current (x axis) graph. Now replace that resistance with another resistance. Plot that as a point on the graph. Do this for a few resistances. You find that these points (each corresponding to a resistance) make a downward sloping line. The line is not horizontal as you might expect, but the voltage seems to change based on the resistance. There is an interesting linear relationship there, sure. But I don't see how Ohm's Law is tested there. Ohm's Law is a statement about how when temperature and resistance is kept constant, the voltage applied across a resistor is directly proportional to the current passing through that resistor. It seems to be a statement involving a single resistor. Once you start measuring different resistances, you don't seem to be testing Ohm's Law but some other linear relationship (which to be honest I haven't been able to clarify to myself). The way I would test Ohm's Law is I would pick a single resistor, and change the voltage across it, and see if that plot of voltage vs current is a line. I would love some help on figuring out what I'm apparently missing. Thanks.