Physics Current Electricity UHS 2022
PMDC Verified Question 55 of 112
What do the substances whose resistance decreases with increase in temperature have?
A
High temperature coefficient
B
Negative temperature coefficient
C
Positive temperature coefficient
D
Zero temperature coefficient
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Negative temperature coefficient
Concept:

The temperature coefficient (\(\alpha\)) denotes the direction and magnitude of resistance change with temperature.

Formula:

$$ \Delta R = R_0 \alpha \Delta T $$

Solution:

  • If resistance decreases as temperature increases, \( \Delta R \) is negative while \( \Delta T \) is positive.


  • This mathematically requires \( \alpha \) to be negative.


  • Substances like semiconductors and insulators possess this Negative temperature coefficient.


Why other options are incorrect:

  • Opt C: Means resistance increases with temperature (like typical metals).


  • Opt D: Means resistance is independent of temperature (like specific alloys e.g., Manganin).

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