Question

A straight wire having mass of 1.2 kg and length of 1 m carries a current of 5A. If the wire is suspended in mid-air by a uniform horizontal magnetic field, then the magnitude of field is then

• A. 0.65 T
• B. 1.53 T
• C. 2.4 T
• D. 3.2 T

Answer 1

Answer: (C)

2.4 T

For mid-air suspension the upward force F on wire due to magnetic field B must be balanced by the force due to gravity, then
$F_m=Mg$

$IlB=mg,B=\frac{mg}{Il}$
Here, $m=1.2kg,g=10m{s}^{-2},I=5A,l=1m$
$B=\frac{1.2\times 10}{5\times 1}=2.4T$