Sponsor Area

Current Electricity

Question
CBSEENPH12039789

A square loop of ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be

  • fraction numerator straight mu subscript straight o li over denominator 2 straight pi end fraction
  • fraction numerator 2 straight mu subscript straight o liL over denominator 3 straight pi end fraction
  • fraction numerator straight mu subscript straight o liL over denominator 2 straight pi end fraction
  • fraction numerator 2 straight mu subscript straight o li over denominator 3 straight pi end fraction

Solution

D.

fraction numerator 2 straight mu subscript straight o li over denominator 3 straight pi end fraction

In the above fig., the direction of currents in a long straight conductor XY and arm AB of a square loop ABCD are in the same direction.
So, there exists a force of attraction between the two conductors, which will be experienced by FAB as,
straight F subscript BA space equals space fraction numerator straight mu subscript straight o space straight I space straight i space straight L over denominator 2 straight pi space open parentheses begin display style straight L over 2 end style close parentheses end fraction
In the case of XY and arm CD, the direction of currents are in the opposite direction.
There exists a force of repulsion which will be experience by CD as,
straight F subscript CD equals space fraction numerator straight mu subscript straight o IiL over denominator 2 straight pi open parentheses begin display style fraction numerator 3 straight L over denominator 2 end fraction end style close parentheses end fraction
Therefore, net force on the loop ABCD is,
Floop = FBA - FCD = fraction numerator straight mu subscript straight o IiL over denominator 2 straight pi end fraction open parentheses fraction numerator 1 over denominator left parenthesis L divided by 2 right parenthesis end fraction minus fraction numerator 1 over denominator left parenthesis 3 L divided by 2 right parenthesis end fraction close parentheses
Floop = fraction numerator 2 straight mu subscript straight o iI over denominator 3 straight pi end fraction