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COMEDK2013PhysicsCurrent Electricity

An unknown resistance R₁ is connected in series with a resistance of 10 ~ . This combination is connected to one gap of a meter bridge, while a resistance R₂ is connected in the other gap. The balance point is at 50 ~cm . Now, when the 10 ~ resistance is removed, the balance point shifts to 40 ~cm . The value of R₁ (in ) is

Options

  1. A20
  2. B10
  3. C60
  4. D40

Correct answer

A. 20

Step-by-step solution

In first case, P=R₁+10, Q=R₂, l=50 ~cm For balanced condition, P Q = l 100-l R₁+10 R₂ = 50 50 R₁+10=R₂ Similarly, for second case, P=R₁, Q=R₂, l=40 ~cm R₁ R₂ = 40 100-40 = 40 60 R₂= 3 2 R₁ Putting value of R₂ from Eq . (ii) in Eq (i), we get aligned R₁+10 &= 3 2 R₁ R₁ &=2 10=20 aligned

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