The resistance of insulators __________

Question

Examoogle · Accepted Answer

Decreases with an increase in temperature

Explanation: Insulators exhibit a negative temperature coefficient of resistance (NTCR), meaning their electrical resistance decreases as temperature increases. Unlike metals, which have a positive temperature coefficient, insulators rely on thermally activated charge carriers to conduct.

Working Principle: In insulators, electrons are bound in the valence band by a large energy gap (forbidden gap). As temperature increases, thermal energy excites some electrons from the valence band to the conduction band. This increase in the concentration of free charge carriers leads to an increase in conductivity and a corresponding decrease in electrical resistance.

Key Formulas: $R_T = R_0 e^{\frac{\beta}{T}}$ — where $R_T$ is resistance at temperature $T$, $R_0$ is reference resistance, and $\beta$ is the material constant.

Key Points: Insulators have a large energy band gap (> 3 eV).; Negative Temperature Coefficient (NTC) is a characteristic property of insulators and semiconductors.; Higher temperatures facilitate the movement of electrons across the forbidden energy gap.; The resistance-temperature relationship is exponential rather than linear.

Advantages: High dielectric strength at low temperatures; Self-insulating properties improve at very low temperatures

Disadvantages: Increased leakage current at high operating temperatures; Risk of thermal runaway in specific insulation materials

Applications: NTC thermistors used for temperature sensing; Electrical insulation systems for power transformers and cables

Additional Info: Most metals (conductors) have a Positive Temperature Coefficient (PTC) of resistance.. Option A is incorrect because it describes the behavior of pure metals.. Option C is incorrect because resistance is rarely constant across temperature variations for dielectric materials.

Answer: B is correct — Insulators have a negative temperature coefficient of resistance, causing their resistance to drop as they become hotter due to increased charge carrier generation.

Exam Tip: Always remember that conductors (metals) have a Positive Temperature Coefficient (PTC), while semiconductors and insulators typically have a Negative Temperature Coefficient (NTC).

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