Concept:Ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across it, provided temperature remains constant.
Mathematically,
V=IR, where
V is voltage,
I is current, and
R is resistance.
Substances that obey Ohm's law are called ohmic (e.g., metals).
Substances that do not obey Ohm's law are non-ohmic (e.g., semiconductors, diodes, gases).
Explanation:• Conducting copper coil: Copper is a metal, so it obeys Ohm's law. It is ohmic.
• Electric heating coil: Made of metal (e.g., nichrome), thus ohmic.
• Semiconductor diode: A diode does not have a linear current‑voltage relationship. It conducts only in one direction and shows a non‑linear curve. Hence it is non‑ohmic.
• Rheostat: Typically made of a coiled metal wire (e.g., copper or nichrome), so it is ohmic.
Answer:Semiconductor diode (Option C) is non‑ohmic.
