NEET 2022 — Physics solution

NEET2022Physics

A wheatstone bridge is used to determine the value of unknown resistance X by adjusting the variable resistance Y as shown in the figure. For the most precise measurement of X, the resistances P and Q :

A
should be approximately equal and are small
B
should be very large and unequal
C
do not play any significant role
D
should be approximately equal to 2X

Solution

At balance, $\frac{P}{Q} = \frac{X}{Y}$ , so $X = \frac{P}{Q} \cdot Y$ .

Sensitivity of the bridge is best when the four arm resistances are comparable in magnitude.

If P and Q are approximately equal, fractional uncertainty in $P / Q$ stays small. Keeping them small (but not so small that currents become impractically large) also minimises the relative error from contact and lead resistances.

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