JEE Main 2017 · 9 Apr · Shift 1 · Physics Q29

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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 :

Meter bridge: resistances P and Q in the gaps of the upper strip, the galvanometer G from their junction to the jockey at N on the wire AB, and a cell E, rheostat Rₕ and key K across AB.

\dfrac{33}5

6 Ω

7 Ω

\dfrac{20}3

Answer and worked solution

Official answer: D

Initially $\dfrac PQ=\dfrac{60}{40}$ , so $Q=\dfrac83$ Ω. Then $\dfrac{4+R}{8/3}=\dfrac{80}{20}=4$ , so $4+R=\dfrac{32}3$ and $R=\dfrac{20}3$ Ω.

Topics:Wheatstone bridge and metre bridge

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JEE Main 2017 · 9 Apr · Shift 1, Physics question 29