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Moving Charges And Magnetism
Question
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A thermocouple force towards the conductor produces an emf of 40 μ V/oC in the linear range of temperature. A galvanometer of resistance 10 Ω whose sensitivity is 1μA/div, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be.

  • 0.5oC

  • 1oC

  • 0.1oC

  • 0.25oC

Answer

D.

0.25oC

For minimum  deflection of 1 division require current =1 μA
Voltage required = iR = 1 x 10 = 10 μV
40 μV = 1oC
10 μV = 1/4 = 0.25oC

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Some More Questions From Moving Charges And Magnetism Chapter

Two moving coil meters, M1 and M2 have the following particulars:
R1 = 10 Ω   N1 = 30,
A1 = 3.6 x 10–3 m2,  B1 = 0.25 T
R2 = 14 Ω;  N2 = 42,
A2 = 1.8 x 10–3 m2, B2 = 0.50 T
(The spring constants k are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of M2 and M1.