Ohm's Law And Resistance

Question

In an experiment to verify Ohm's law, a conductor carries a steady current of 0.5 A when a potential difference of 3 V is applied across its ends at constant temperature.

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Ohm's law, as verified experimentally in NCERT Class 12, Chapter 3, states that at constant temperature the current through a conductor is directly proportional to the potential difference across it, so the resistance is $R=\frac{V}{I}$. Substituting the measured potential difference $V=3$ V and current $I=0.5$ A gives $R=\frac{3}{0.5}=6$ ohm. The graph of $V$ against $I$ for such an ohmic conductor is a straight line through the origin, and its slope equals this resistance. The value 1.5 ohm is wrong because it multiplies voltage by current rather than dividing, misapplying the relation. The value 3.5 ohm is wrong because it adds voltage and current, which is dimensionally meaningless. The value 0.17 ohm is wrong because it inverts the ratio, computing current divided by voltage, which gives conductance, not resistance. A magnitude check confirms that dividing 3 volts by half an ampere sensibly yields 6 ohm, a reasonable laboratory resistance, and the units volt per ampere correctly reduce to ohm.

Ohm's Law And Resistance

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