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Question
In the meterbridge experimental set up, shown in the figure, the null point ‘D’ is obtained at a distance of 40 cm from end A of the meterbridge wire. If a resistance of 10Ω is connected in series with R1, null point is obtained at AD = 60 cm. Calculate the values of R1 and R2.
Solution
Considering both the situations and writing them in the form of equations
Let R' be the resistance per unit length of the potential meter wire,
`R_1/R_2 = (R' xx 40)/(R'(100 -40) ) = 40/60 = 2/3`
`(R_1 + 10)/R_2 = (R' xx 60)/(R'(100 -60)) = 60/40 = 3/2`
`R_1/R_2 = 2/3 -------- (1)`
`(R_1 +10)/R_2 = 3/2 ---------(2)`
Putting the value of R1 from equation (1) and substituting in equation (2)
`2/3 + 10/R_2 = 3/2`
`R_2 = 12Ω`
Reca;;omg equation (1) again
`R_1/12 = 2/3`
`R_1 = 8Ω`
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