Resistivity of copper, nichrome and a semiconductor varies with temperature respectively as
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Exponential increase, linear and exponential decrease
The way resistivity changes with temperature differs for a pure metal, an alloy and a semiconductor.
Copper (pure metal): the resistivity rises with temperature along a curve that bends upward over a wide range of temperature; it is close to linear only over a limited range. The options describe this rise as an exponential increase.
Nichrome (alloy): its temperature coefficient of resistivity is very small, so the resistivity shows only a weak, nearly linear rise with temperature. This is why nichrome is used in heating elements and standard resistors.
Semiconductor: the number of charge carriers grows rapidly as the temperature rises, so the resistivity shows an exponential decrease.
Option (1) Linear, exponential increase and exponential decrease — Incorrect. It calls nichrome's variation an exponential increase, but nichrome's resistivity rises only weakly and almost linearly.
Option (2) Exponential increase, linear and exponential decrease — Correct. Copper rises along an upward-bending curve, nichrome rises nearly linearly, and the semiconductor falls exponentially.
Option (3) Exponential increase, exponential decrease and linear — Incorrect. Nichrome is a metallic alloy, so its resistivity increases with temperature, and a semiconductor's resistivity is not linear in temperature.
Option (4) Linear, exponential decrease and exponential increase — Incorrect. A semiconductor's resistivity decreases with temperature, and nichrome's does not decrease.