For a certain device, the current is proportional to the voltage up to 3 V. The current is 30 mA at 3 V. At 6 V, the current is found to be 45 mA. Compared with the value expected from Ohm’s law, the current at 6 V is less by
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 25%
Up to 3 V the device obeys Ohm’s law, so \( V/I \) stays constant. If this had continued up to 6 V, doubling the voltage would have doubled the current.
\( \begin{aligned} I_{Ohm} &= 30\times\frac{6}{3} \\ &= 60\ \mathrm{mA} \end{aligned} \)
The actual current at 6 V is 45 mA.
\( \begin{aligned} \text{Percentage less} &= \frac{60-45}{60}\times100 \\ &= \frac{15}{60}\times100 \\ &= 25\% \end{aligned} \)
From the above, the current at 6 V is 25% below the Ohm’s law value. Hence, above 3 V the device does not obey Ohm’s law.
NCERT (2026-27):
Limitations of Ohm’s Law – “… there do exist materials and devices used in electric circuits where the proportionality of V and I does not hold. The deviations broadly are one or more of the following types: (a) V ceases to be proportional to I …”