Q.

Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I1 and I2 currents, respectively. Point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be               [2014]
 

1 μ02πd(I1I2)  
2 μ02πd(I1+I2)  
3 μ02πd(I12-I22)  
4 μ02πd(I12+I22)1/2  

Ans.

(4)

The magnetic field at the point P, at a perpendicular distance d from O in a direction perpendicular to the plane ABCD due to currents through AOB and COD are perpendicular to each other. Hence,

B=(B12+B22)1/2

=[(μ04π2I1d)2+(μ04π2I2d)2]1/2

=μ02πd(I12+I22)1/2