A current carrying wire kept in a uniform magnetic field, will experience a maximum force when it is

Magnitude of force on a current carrying conductor kept in internal magnetic field,
$\mathrm{F}=\text{ B.I.l }\sin \mathrm{\theta }$
where B$\to$magnetic field, I $\to$ current, l $\to$length of conductor
Force would be maximum when sin $\theta$ is maximum. So, sin $\theta$ must be equal to 1, Thus, $\mathrm{\theta }=\frac{\mathrm{\pi }}{2}$
Hence, current carrying wire is kept perpendicular to the magnetic field to experience maximum magnetic force.