A plane square loop PQRS of side 'a' made of thin copper wire has 'n' turns and it carries a direct current 'I' ampere in the direction shown in the adjoining figure. This wire loop is placed in a magnetic field of flux density 'B' tesla, which is directed perpendicularly in to the plane of the loop. What is the torque acting on the loop?
A plane square loop PQRS of side 'a' made of thin copper wire has 'n' turns and it carries a direct current 'I' ampere in the direction shown in the adjoining figure. This wire loop is placed in a magnetic field of flux density 'B' tesla, which is directed perpendicularly in to the plane of the loop. What is the torque acting on the loop?
The correct option is D Zero
The magnetic force on the side PQ of the loop is nIaB and is directed upwards through the midpoint of PQ in accordance with Fleming's left hand rule (motor rule). The magnetic force on the side RS of the loop is nIaB itself; but it is directed downwards through the midpoint of RS. These two forces cannot produce a torque since they have the same line of action.
The magnetic force on the side QR of the loop is nIaB and is directed leftwards through the midpoint of QR. The magnetic force on the side SP of the loop is nIaB itself; but it is directed rightwards through the midpoint of SP. These two forces also cannot produce a torque since they have the same line of action.
Thus the net torque acting on the loop is zero
Zero
The magnetic force on the side PQ of the loop is nIaB and is directed upwards through the midpoint of PQ in accordance with Fleming's left hand rule (motor rule). The magnetic force on the side RS of the loop is nIaB itself; but it is directed downwards through the midpoint of RS. These two forces cannot produce a torque since they have the same line of action.
The magnetic force on the side QR of the loop is nIaB and is directed leftwards through the midpoint of QR. The magnetic force on the side SP of the loop is nIaB itself; but it is directed rightwards through the midpoint of SP. These two forces also cannot produce a torque since they have the same line of action.
Thus the net torque acting on the loop is zero
