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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.
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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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