In a metre bridge experiment, the null point should ideally be obtained in the middle one-third (between 34 cm and 66 cm) of the wire because:
APercentage errors in $\ell_x$ and $\ell_R$ become minimum and nearly equal
BContact resistance is zero there
CThe wire is most uniform there
DThe galvanometer is most sensitive there
Answer & Solution
Correct answer: A. Percentage errors in $\ell_x$ and $\ell_R$ become minimum and nearly equal
Choosing R so that the null point falls in the central one-third makes $\ell_x$ and $\ell_R$ comparable in length — the fractional measurement error is then small and nearly the same for both, minimising the propagated error in $X$.
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