A conducting 1 rod of mass ‘m’ and length ‘l’ is changed horizontally with the help of two insulating threads such that the rod is along east-west direction. Now current I is set up form west to east direction. What should be magnitude and direction of magnetic field. So that tension in the threads becomes zero?

$B=\frac{mg}{Il}$, towards north

The correct answer is option (1) : $B=\frac{mg}{Il}$, towards north

$mg=B/L$

$B=\frac{mg}{IL},$ towards north to ensure that magnetic force upwards.