Two resistances X and Y in the two gaps of a meter-bridge gives a null...
Explanation:
Meter Bridge Experiment
Meter bridge experiment is an experiment which is used to find the resistance of a wire. In this experiment, the resistance of an unknown resistor is compared with the known resistance of a wire.
Null Point
The point on the wire where there is no flow of current is known as the null point. At this point, the potential difference across the two points on the wire is zero.
Given
Let X and Y be the resistance in the two gaps of the meter bridge. Let the length of the wire be L. The null point divides the wire in the ratio 2:3, which means that the distance of the null point from X is 2L/5 and the distance of the null point from Y is 3L/5.
Equations
Using the principle of Wheatstone bridge, we can write the following equations:
X/(L/5) = Y/(4L/5) ----- (1)
X/(2L/5) = Y/(3L/5) ----- (2)
From equation (1), we get X = (L/5) Y/(4L/5) = Y/4
From equation (2), we get X = (2L/5) Y/(3L/5) = (4/3)Y
Equating the above two equations, we get:
Y/4 = (4/3)Y
Y = 16Ω
X = Y/4 = 4Ω
Increased Resistance
When each resistance is increased by 3Ω, the new resistance of X is 7Ω and the new resistance of Y is 19Ω.
Equations for New Null Point
Let the new null point be at a distance of x from X. Then, the new null point will be at a distance of (L-x) from Y.
Using the principle of Wheatstone bridge, we can write the following equations:
7/(L-x) = 19/x ----- (3)
7/(5L/6 - x) = 19/(L/6 + x) ----- (4)
From equation (3), we get x = 3L/8
From equation (4), we get x = L/4
Answer
Therefore, the value of X is 4Ω and the value of Y is 16Ω.