A current of 1 A is flowing on the sides of an equilateral triangle of side $4.5 \times 10 ^ { - 2 } \mathrm {~m}$. The magnetic field at the centre of the triangle will be:\\
(1) $4 \times 10 ^ { - 5 } \mathrm {~Wb} / \mathrm { m } ^ { 2 }$\\
(2) Zero\\
(3) $2 \times 10 ^ { - 5 } \mathrm {~Wb} / \mathrm { m } ^ { 2 }$\\
(4) $8 \times 10 ^ { - 5 } \mathrm {~Wb} / \mathrm { m } ^ { 2 }$