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In a meter bridge experiment resistances are connected as shown in the figure. Initially resistance P = 4 Ω and the neutral point N is at 60 cm from A . Now an unknown resistance R is connected in series to P and the new position of the neutral point is at 80 cm from A . The value of unknown resistance R is -

Options

  1. A33 5 Ω
  2. B6 Ω
  3. C20 3 Ω
  4. D7 Ω

Correct answer

C. 20 3 Ω

Step-by-step solution

Given initially a resistance P   =   4   Ω is connected in the left gap and let Q is connected in the right gap of meter bridge and the null point is obtained at 60   cm , From the balanced condition of the Wheatstone bridge P Q = R S     . . . 1 Let ρ is the resistance per unit length of meter bridge wire than For wire A N , P = ρ l = 40   ρ       ∵   l   =   40   cm And for NB wire Q   =   ρ 100 - l Q =

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