Question : A resistance R is to be measured using a meter bridge. Student choose the standard resistance S to be 100Ω. He finds the null point at l1=2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way?
a) He should measure l1 more accurately.
b) He should change S to 1000Ω and repeat the experiment.
c) He should change S to 3Ω and repeat the experiment.
d) He should give up hope of a more accurate measurement with a meter bridge.
Doubt by Parish
Solution :
We know,
For Meter Bridge
R/S = l/(100-l)
Here
R = Unknow Resistance = ?
S = 100 Ω
l1 = 2.9 cm
R/S = l1/(100-l1)
R/100 = 2.9/(100-2.9)
R/100 = 2.9/97.1
R = (29×100)/971
R = 2900/971
R = 2.9866 Ω
We know, that the value of unknown resistance is accurate when the null point is obtained between the 40 cm and 60 cm of the meter bridge wire and this can be done when the resistance values of R and S are nearly in the same order. As we can see here that R=2.98 Ω but S=100Ω so the value of R can be accurately determined if the resistance value of S should be reduced to around 2.98 Ω.
Hence, the c) would be the correct option.
