Ohm's Law

Question

A nichrome heating element draws a steady current of 2.5 A when connected across a 220 V domestic supply. What is its operating resistance?

RankGuru · Accepted Answer

Ohm's Law expresses that, for a conductor at constant temperature, the current flowing through it is directly proportional to the applied potential difference, so the ratio $V/I$ defines a fixed resistance $R$. For an ohmic device such as a nichrome element operating in steady state, this resistance is the meaningful conductive opposition the circuit experiences. Rearranging $V = IR$ gives $R = V/I$. Substituting the supply voltage $V = 220$ V and the measured current $I = 2.5$ A yields $R = 220/2.5 = 88\;\Omega$. The option 55 $\Omega$ is incorrect because it would demand a current of 4 A, far above the stated value. The option 110 $\Omega$ is wrong since it corresponds to a current of only 2 A. The option 220 $\Omega$ is wrong because numerically equating resistance with voltage ignores the current entirely. This is the standard NCERT treatment of resistance as the constant of proportionality in Ohm's Law. A plausibility check confirms the answer: 88 $\Omega$ carrying 2.5 A indeed dissipates about 550 W, a typical rating for a heating appliance.

Ohm's Law

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