1.

A long current carrying wire , carrying current I_(1) such that I_(1) is flowing out from the plane of paper is placed at O. A steady state current I_(2) is flowingin the loop ABCD

Answer»

the net FORCE is zero
the net TORQUE is zero
as seen from `O` , the loop will rotate in CLOCKWISE along `OO'` axis
as seen from `O`, the loop will rotate in anticlockwise direction along `OO'` axis

Solution : Net force on the loop :
Force on `AB` .
` dF xxBxx sin 0@)= 0`
Force on CD `: Similarly the magnetic field due to current `I_(1)` is along ` DC` . Because ` theta = 180^(@)` here , therefore force on ` DC` is zero .
Force on `BC ` : Consider a small element `dl`.
` dF = I_(2) dl B_(1) sin 90^(@) rArr dF = I_(2) dl B_(1) `
By Fleming's left hand rule , the direction of this force is perpendicular to the plane of the paper directed outwards .
Force on ` AD` : ` dF = I_(2) dl B_(1) sin 90^(@) rArr dF = I_(2) dl B_(1) `
By Fleming's left hand rule , the direction of this force is perpendicular to theplane of paper directed inwards. Since the current elements are located symmetrical to current ` I_(1) , therfore force on `BC` will cancel out the effect of force on ` AD`.
rArr Net force on loop ` ABCD` is zero.
` NEt Torque on the loop : Theforce on ` BC and AD` will create a torque on ` ABCD` in clockwise direction about ` OO` as seen by the observer at `O`.




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