A straight wire of mass 500 g and length 7 m carries a current of 1.4 A. It is suspended in mid air by a uniform horizontal magnetic field B perpendicular to the length of the wire. The magnitude of magnetic field is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 0.5 T
Using Lorentz force,
$F_L=ILB\sin θ$
for $\sin 90°=1$,
$F=ILB$
and,
$F_{gravity}=mg$
$=0.5×9.8=4.9N$
and,
$F_L=F_G$
$1.4×7×B=4.9$
$B=0.5T$