Q. A thermocouple of negligible resistance produces an e.m.f. of 40 µV/°C in the linear range of temperature. A galvanometer of resistance 10 ohm whose sensitivity is 1 µA/div, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be
A) 0.1°C
B) 0.25°C
C) 0.5°C
D) 1°C
Explanation
[Solution from source] The smallest detectable current is 1 µA (one division), so the smallest detectable emf is 1 µA × 10 Ω = 10 µV. With 40 µV per °C, ΔT = 10/40 = 0.25°C. Answers like 0.1°C or 0.5°C come from mixing up the ratio. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.