Which one of the following devices is non-ohmic ?

Ohmic devices are those that follow Ohm's law, where the potential difference across the conductor is directly proportional to the current through it, provided temperature remains constant [2]. Conducting copper coils and rheostats (variable resistors) are typically ohmic as they consist of metallic conductors like copper or platinum, whose resistance is almost linearly dependent on temperature [3]. Electric heating coils, often made of alloys, also maintain ohmic behavior despite high resistivity [3]. In contrast, semiconductor diodes are non-ohmic devices. They are active electronic components that exhibit a non-linear relationship between voltage and current. Unlike simple resistors, the current in a diode does not vary linearly with the applied voltage, and its conductivity is significantly altered by doping and junction properties rather than just metallic resistance [2].

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > What you have learnt > p. 192
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > I = V/R (11.7) > p. 176
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Activity 11.3 > p. 179