Physics-
General
Easy

Question

In the given circuit the current I1 is

  1. 0.4 A    
  2. – 0.4 A    
  3. 0.8 A    
  4. – 0.8 A    

The correct answer is: – 0.4 A


    The circuit can be simplified as follows

    Applying KCL at junction A
    i subscript 3 end subscript equals i subscript 1 end subscript plus i subscript 2 end subscript.….(i)
    Applying Kirchoff’s voltage law for the loop ABCDA
    negative 30 i subscript 1 end subscript minus 40 i subscript 3 end subscript plus 40 equals 0
    rightwards double arrow negative 30 i subscript 1 end subscript minus 40 left parenthesis i subscript 1 end subscript plus i subscript 2 end subscript right parenthesis plus 40 equals 0
    rightwards double arrow 7 i subscript 1 end subscript plus 4 i subscript 2 end subscript equals 4 .….(ii)
    Applying Kirchoff’s voltage law for the loop ADEFA.
    negative 40 i subscript 2 end subscript minus 40 i subscript 3 end subscript plus 80 plus 40 equals 0
    rightwards double arrow negative 40 i subscript 2 end subscript minus 40 left parenthesis i subscript 1 end subscript plus i subscript 2 end subscript right parenthesis equals negative 120
    rightwards double arrow i subscript 1 end subscript plus 2 i subscript 2 end subscript equals 3…….(iii)
    On solving equation (ii) and (iii) i subscript 1 end subscript equals negative 0.4 A.

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