A resistance R is to be measured using a meter bridge, student chooses 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 I₁ more accurately(b) He should change 5 to 1000Ω and repeat the experiment(c) He should change S to 3v and repeat the experiment(d) He should given up hope of a more accurate measurement with a meter bridge
Answers
In this problem, the concept of Wheatstone Bridge is applied .
Wheatstone bridge is an arrangement of four resistances which can be used to measure one unknown resistance when three of them are known .
The condition of balancing of Wheatstone Bridge is -
The Wheatstone Bridge is said to be balanced when the ratio of the resistances in same branch is equal .
We can say that - R/S = l₁/(100 - l₁)
We can minimise the percentage error if we adjust the balance point near the middle of the bridge . So , a value of S has to be chosen.
As, R/S = l₁/(100 - l₁)
Here, R/S = 2.9/(100 - 2.9)
= 2.9/97.1
So, the value of S will be approximate 33 times to that of R.
So, if we have to make this ratio 1:1, we have to reduce the value of S approximate 1/33 times .
As, student chooses the standard resistance S to be 100Ω.
So, the changed value of S = 100/33
= 3 ohm
Hence, the correct option is (c) He should change S to 3 Ω and repeat the experiment .