question_answer

Two long parallel wires are at a distance 2d apart. They carry steady equal currents flowing out of the plane of the paper, as shown. The variation of the magnetic field B along the line XX? is given by                         [IIT-JEE (Screening) 2000]

A)                    

B)              

C)                      

D)               

Correct Answer: B

Solution :

           If the current flows out of the paper, the magnetic field at points to the right of the wire will be upwards and to the left will be downward. Now magnetic field at C, is zero. The field in the region \[B{X}'\]will be upwards (+ve) because all points lying in this region are to the right of both the wires. Similarly, magnetic field in the region AX will be downwards (? ve). The field in the region AC will be upwards (+ve) because points are closer to A compared to B. Similarly magnetic field in region BC will be downward (?ve). Graph  satisfies all these conditions.