Which one of the following statements regarding Ohm’s law is not correct ?
[amp_mcq option1=”Ohm’s law is an assumption that current through a conductor is always directly proportional to the potential difference applied to it.” option2=”A conducting device obeys Ohm’s law when the resistance of a device is independent of magnitude and polarity of applied potential difference.” option3=”A conducting material obeys Ohm’s law when the resistance of material is independent of the magnitude and direction of applied electric field.” option4=”All homogeneous materials obey Ohm’s law irrespective of whether the field is within range or strong.” correct=”option4″]
This question was previously asked in
UPSC NDA-2 – 2019
Statements A, B, and C describe aspects of Ohm’s law or materials obeying it. Statement A describes Ohm’s law as the proportionality between V and I (though the “always” can be debated depending on interpretation, compared to D it’s less definitively wrong). Statements B and C correctly define an ohmic device/material as one whose resistance is independent of the magnitude and direction of the applied potential difference/electric field. Statement D is a universal claim that is false. Many homogeneous materials (e.g., semiconductors, diodes, electrolytes) do *not* obey Ohm’s law. Even ohmic materials like metals can deviate from Ohm’s law at very high electric fields or extreme temperatures.