Physics · Current Electricity · NEET
The actual statement of Ohm's law is the proportionality: V is proportional to I (at constant temperature and physical conditions). V = IR is the equation you get after writing R as the constant of proportionality. So V = IR by itself is really just the definition of resistance (R = V / I) and is always true for any device. The physics content of Ohm's law is the extra claim that R stays constant when V and I change. NEET loves this distinction.
They are the same relation rearranged. V = IR gives voltage when you know current and resistance. I = V / R gives current when you know voltage and resistance. R = V / I gives resistance. Learn all three forms; NEET numericals expect you to pick whichever isolates the unknown.
Inside a conductor, a bigger potential difference V makes a stronger electric field, which pushes the free electrons faster (higher drift velocity), so more charge flows per second — a bigger current I. If temperature is fixed, doubling V doubles I, keeping V / I constant. That constant is R.
Temperature (and physical state) must stay constant. If current heats the wire, R rises and the V-I line bends, so the material stops being ohmic. That is why the statement always adds 'at constant temperature'.
No. Ohmic conductors (like metallic wires at fixed temperature) give a straight V-I line through the origin. Non-ohmic devices (diodes, filament bulbs, electrolytes, semiconductors) give curved V-I graphs, so V = IR is not obeyed as a constant-R law even though R = V / I is still defined at each point.
In the two circuits shown (same 10 V cell, same 10 ohm resistor; ideal meters, only the order of the voltmeter V and ammeter A swapped), the readings of the voltmeters and ammeters will be:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
At constant temperature, the current through a conductor is directly proportional to the potential difference across it, i.e. V is proportional to I, so V = IR where R is the resistance.
V = IR, where V is the potential difference in volts, I is the current in amperes, and R is the resistance in ohms. Rearranged: I = V / R and R = V / I.
V is the potential difference (voltage) across the conductor in volts (V). I is the current through it in amperes (A). R is the resistance in ohms (symbol capital omega).
Yes. For an ohmic conductor the V-I graph is a straight line through the origin, and its slope equals R = V / I. A steeper line means higher resistance.
It was discovered by the German scientist G. S. Ohm in 1826-1828, before the electron theory of current was known. The SI unit of resistance, the ohm, is named after him.
