In an NTC sensor, what happens to resistance as temperature rises?

• A. Increases.
• B. Decreases.
• C. Remains constant.
• D. First increases then decreases.

Answer: (B)

NTC thermistors have a negative temperature coefficient, so their resistance falls as temperature increases. In semiconducting materials, raising temperature excites more charge carriers, increasing conductivity and lowering resistance. The relationship is steep, often described by R(T) ≈ R0 exp[B(1/T − 1/T0)], which shows a clear decrease in resistance with rising temperature. This behavior is what makes NTC sensors useful for temperature measurement, and it contrasts with PTC devices, where resistance increases with temperature.