Four very long, current carrying wires in the same plane intersect to form a square `40.0 cm` on each side as shown in figure. Find the magnitude and direction of the current `I` so that the magnetic field at the centre of square is zero. Wires are insulated from each other.

Options

A. `4.0A` toward the bottom
B. `2.0A` toward the bottom
C. `2.5A` toward the bottom
D. `2.6A` toward the bottom

Answer

B

Explanation

(b) `BpropI`, because distance of centre for all wires is zero.
`B_1=kI_1=10k ox, B_2=kI_2=8k ox`
`B_3=kI_3=20k odot, B_4=kI_4`
Now `B_1+B_2+B_3+B_4=0`
`implies (10K+8K-20K)ox+kI_4=0`
`implies kI_4=2kox`
`implies I_4=2A` towards the bottom.