Current I flows around the wire frame along the edge of a cube as shown in Fig. Point P is the centre of the cube. The incoming and outgoing wires have orientation toward P. Then,

Options

A. the magnetic field at P is toward +y direction
B. the magnetic field at P is toward -y direction
C. the unit vector of magnetic field at P is `-1/sqrt2(hati-hatj)`
D. the magnitude of magnetic field at P is `(4sqrt2mu_0I)/(3pia)`

Answer

A

Explanation

(a) The resultant figure can be redrawn as in Fig.
The field at P due to upper and lower squres will cancel
out. Resultant field at P will be due to the squres BCGF as shown in the figure . Solve to get, `B_P=(4mu_0I)/(pisqrt3a)`