In the post office box circuit, 10 Ω Ω plug is taken out in arm AB and 100 Ω Ω plug is taken out in arm BC. If the unknown resistor is kept in melting ice chamber, 600 Ω Ω resistance is required in arm AD for zero deflection in galvanometer. Now if the unknown resistor is kept at 100° C (steam chamber), 630 Ω Ω resistance is required in arm AD for zero deflection. Temperature coefficient of resistance of the unknown wire is:
Text Solution
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= 
⇒ 
= 
X = 6000 Ω Ω
For second case
= 
⇒ 
= 
⇒ X = 6300 Ω Ω
R f = R 0 (1 + α Δ T)
6300 = 6000 (1 + α (100))
Α = 5 × × 10 –4 / C°
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