  Question

V=IR, from this equation it's clear that V is directly proportional to I and R.. I=V/R, from this equation it's clear that I is directly proportional to V and inversely proportional to R. But when V is directly proportional to R and I is directly proportional to V then why is I not directly proportional to R?

Solution

By ohm's law, voltage is directly proportional to current only and not resistance, and the R in the equation is the proportionality constant, whose value depends on the circuit. Like the proportionality constant in the equation of gravitation i.e. F = GMm/ r2 so we cannot say that voltage is directly proportional to R, although it is quite clear from the equation. This is because we cannot keep the current constant and let the Resistance define the voltage and regarding the statement, I is directly proportional to V, it will be more suitable to understand if you write in this form " I/V is a constant or V/I is constant.Physics

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