Which one of the following devices is non-ohmic ?

Conducting copper coil

Electric heating coil

Semi conductor diode

Rheostat

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This question was previously asked in

UPSC NDA-1 – 2018

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An ohmic device obeys Ohm’s Law (V = IR) where resistance (R) is constant regardless of voltage (V) or current (I). A non-ohmic device does not obey Ohm’s Law; its resistance varies with the applied voltage or current.
– Conducting copper coil (A) and Electric heating coil (B) (like Nichrome wire) are generally considered ohmic conductors, although their resistance can change with temperature.
– A Rheostat (D) is a variable resistor, but for any fixed resistance setting, it acts as an ohmic resistor.
– A Semiconductor diode (C) is a device that exhibits a highly non-linear current-voltage characteristic. It conducts current effectively in only one direction (forward bias) and only above a certain threshold voltage. Its resistance changes dramatically depending on the applied voltage and direction. Therefore, it is a classic example of a non-ohmic device.

– Ohmic devices have constant resistance independent of voltage or current.
– Non-ohmic devices have resistance that varies with voltage or current.
– Metal conductors are typically ohmic (assuming constant temperature).
– Semiconductor devices like diodes and transistors are typically non-ohmic.

The V-I graph for an ohmic device is a straight line passing through the origin with a slope equal to the resistance. The V-I graph for a non-ohmic device is curved. Examples of non-ohmic devices include vacuum tubes, gas discharge lamps, and semiconductor components like diodes and transistors.

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