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Current Electricity

Question
CBSEENPH12039859

A ring is made of wire having a resistance Ro = 12Ω. Find the points A and B, as shown in the figure, at which a current carrying conductor should be connected so that the resistance R of the subcircuit between these points is equal to 8/3Ω

  • straight l subscript 1 over straight l subscript 2 space equals 5 over 8
  • straight l subscript 1 over straight l subscript 2 space equals space 1 third
  • straight l subscript 1 over straight l subscript 2 space equals space 3 over 8
  • straight l subscript 1 over straight l subscript 2 space equals 1 half

Solution

D.

straight l subscript 1 over straight l subscript 2 space equals 1 half We space knows space straight R proportional to straight I
Here comma space straight R subscript 1 plus straight R subscript 2 space equals 12 straight capital omega
and space fraction numerator straight R subscript 1 plus straight R subscript 2 over denominator straight R subscript 1 plus straight R subscript 2 end fraction space equals space 8 over 3 straight capital omega
rightwards double arrow space straight R subscript 1 straight R subscript 2 space equals space 32 space straight capital omega
We space get comma space straight R subscript 1 space equals space 8 space and space straight R subscript 2 space equals space 4
Again comma space straight R subscript 1 space equals space fraction numerator 12 space straight l subscript 1 over denominator straight l subscript 1 plus straight l subscript 2 end fraction
and space straight R subscript 2 space equals fraction numerator 12 space straight l subscript 2 over denominator straight l subscript 1 plus straight l subscript 2 end fraction
Hence comma space fraction numerator straight l subscript 1 over denominator straight l subscript 2 space end fraction space equals 1 half