Figure `6.46`, shows a wheatstone net, with `P = 1000 Omega`,`Q = 10.0 Omega`,`R`(unknows), `S` variable and near `150 Omeag` for balance. If the connections across `A,C` and `B,D` are interchanged, the error range in `R determination would

Options

A. remain unaffected
B. increase substantially
C. increase marginally
D. decrease substantially

Answer

D

Explanation

`R` is the order of `15,000 Omega` The junctions of the heighest two an dthe lowest two resistances are `A` and `C`, and for better sensitivity, the galvanometer will be between these. So, error will decrease with the suggested interchange.
Alternatively : Let `R` be not exactly `15,000 Omega`. Then some potential difference will be creates between points `B` and `D`. Let it be `Delta V_(1)`. Now suppose the connections are interchanged, then the same type of potential difference will be created between points `A` and `C`. Let it be `Delta V_(2)`. So larger current will flow through galvanometer in the second case telling us that value of `R` needs to be changed. And we will try to put more accurate value of `R`. In this way, error will decrease.