Ohm's law is not applicable to

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semi-conductors

Explanation: Ohm's law states that the current flowing through a conductor is directly proportional to the voltage applied across its ends, provided physical conditions like temperature remain constant. This linear relationship ($V = IR$) does not hold for devices such as semiconductors, vacuum tubes, or electrolyte solutions, which exhibit non-linear voltage-current characteristics.

Working Principle: In metallic conductors, the carrier density and scattering mechanisms remain largely constant with applied voltage. In semiconductors, however, the charge carrier concentration is temperature-dependent and governed by the exponential barrier height in p-n junctions, resulting in a non-linear $I-V$ curve that violates the linear assumption of Ohm's law.

Key Formulas: $V = IR$ — Ohm's Law (Linear); $I = I_0(e^{\frac{qV}{kT}} - 1)$ — Shockley Diode Equation (Non-linear)

Key Points: Ohm's law is valid only for Ohmic conductors where the resistance is independent of the applied voltage.; Semiconductors like diodes and transistors have $I-V$ characteristics that are exponential or logarithmic.; Non-ohmic devices do not maintain a constant ratio of $V/I$ as the operating point changes.; Ohm's law is a limiting case and not a fundamental universal law of physics.

Advantages: Simplicity in analyzing DC circuits; Predictable power dissipation in resistive loads

Disadvantages: Cannot be used to model active components like transistors; Fails under varying temperature or high-frequency conditions

Applications: DC circuit analysis; Resistance measurement; Power system load flow studies

Additional Info: Option A: DC circuits are typically analyzed using Ohm's law.. Option B & C: These relate to practical limitations of the component's thermal capacity, not a violation of the fundamental principle of the material property.. A device is Ohmic if its V-I graph is a straight line passing through the origin.

Answer: D is correct — Semiconductors are non-ohmic devices because their current-voltage relationship is non-linear and governed by junction physics rather than a constant resistance.

Exam Tip: Always verify if a device is 'passive' or 'active' when considering Ohm's law applications; active devices like BJTs or MOSFETs are inherently non-ohmic.

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