Why is resistance independent of voltage and current

Question

So in my textbook i read as voltage is proportional to current the resistance is Constant because resistance is really just a ratio of p.d /I , then the book said that Resisitance is independent of pd and I ?????? My doubt is how is that possible as the very definition of resistance is the ratio of pd/I ????? Thank you or rather after concentrating a bit more i came up with this reason: the resistance is independent of voltage and current only in ohmic components as when V is proportional to I , resistance is CONSTANT and that means no amount of increasing or decreasing voltage and current can change anything in resistance as it will always be constant as long as PD is proportional to I . Is this reason the right answer?

Thank you once again in advance

Answer 1

Yes, that's the right idea. The resistance is a constant, more like a material property of the circuit wire itself. R tells you how much current is able to flow in response to a voltage driving the circuit (you mentioned PD is proportional to I---R is the proportionality constant).

You can compare it to water flowing through a pipe. Voltage = pressure from the pump, current = flow rate of water, resistance = size of the pipe (e.g. bigger pipes have less resistance because they allow more water to flow). Changing the pump pressure will never affect the size of the pipe, only push more/less water through.

https://en.wikipedia.org/wiki/Hydraulic_analogy