Physics · Current Electricity · NEET
No, and NEET tests this. Resistance R is a property of a specific piece of wire and changes with its length and area. Resistivity (rho) is a property of the material only and stays the same no matter the shape. They are linked by R = rho x L / A. So copper always has the same resistivity, but a copper wire's resistance depends on how long and thick it is.
A conductor has a resistance of 1 ohm when a voltage of 1 volt across it drives a current of exactly 1 ampere through it. In formula form: 1 ohm = 1 volt / 1 ampere. So the ohm just measures how much 'push' (volts) you need for 1 amp of current to flow.
For an ideal (ohmic) conductor at fixed temperature, resistance is constant. If you increase V, the current I increases in the same ratio, so R = V/I stays the same. Resistance really depends on the material, length, area and temperature of the conductor, not on how much voltage you apply. This is a common trap: raising the battery voltage does not raise the wire's resistance.
Use R = rho x L / A. A longer wire (larger L) means electrons collide with more atoms on the way, so R increases with length. A thinner wire (smaller area A) squeezes the electrons through a narrow path, so R increases when area decreases. Think of a long, narrow water pipe: harder for water to flow.
The quantity resistance is written with the capital letter R in equations. Its SI unit, the ohm, uses the Greek capital letter omega, written as the symbol Ω. So you might write R = 5 Ω, meaning a resistance of five ohms.
No. NCERT is clear that R = V/I is the definition of resistance and applies to every conducting device, whether it obeys Ohm's law or not. Ohm's law is the stronger extra claim that R stays constant when V changes. A diode does not obey Ohm's law, yet at any point you can still find its resistance as V/I.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Resistance is the opposition offered by a conductor to the flow of electric current through it, defined as R = V / I, the ratio of the potential difference across it to the current in it.
The SI unit of resistance is the ohm, symbol Ω. One ohm equals one volt per ampere (1 Ω = 1 V / 1 A).
Resistance is denoted by R in equations, and its unit ohm is denoted by the Greek letter omega, Ω.
Resistance depends on the material (through its resistivity), the length L (R increases with L), the cross-sectional area A (R decreases as A increases) and the temperature. It follows R = rho x L / A.
Resistance is a scalar quantity. It has only magnitude and no direction, and is always positive for ordinary conductors.
