In a Wheatstone’s meter-bridge experiment, the null point is obta… - Vidyadip

Question

In a Wheatstone’s meter-bridge experiment, the null point is obtained in middle one third portion of wire. Why is it recommended?

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Answer

The value of unknown resistance $X$, may not be accurate due to non-uniformity of the bridge wire and development of contact resistance at the ends of the wire.
To minimise these errors, the value of R is so adjusted that the null point is obtained in the middle one-third of the wire (between $34\ cm$ and $66\ cm$) so that the percentage errors in the measurement of $I_X$ and $I_R$ are minimum and nearly the same.

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