Explanation:
In a rectangular loop of wire, a counter-clockwise current flows in a uniform magnetic field pointing towards right.
There are four sides of the rectangular loop ab, bc, cd and da. Lets analyze each side.
Force on section ab:
The force is zero since the wire is parallel to magnetic field
Fab = 0
Force on section bc:
Fbc = BIL
Since the current I is moving upwards and magnetic field is to the right then force F points into the screen.
Force on section cd:
The force is zero since the wire is parallel to magnetic field
Fcd = 0
Force on section da:
Fda = -Fbc
Since the current I is moving upwards and magnetic field is to the right then force F points out of the screen.
The net force acting on the rectangular loop is
Fnet = Fab + Fbc + Fcd + Fda = 0
0 + Fbc + 0 + Fda = 0
Fda = -Fbc
