Question

A straight wire of mass $200$g and length $1.5$m carries a current of $2$A. It is suspended in mid-air in a uniform horizontal magnetic field $B$. The magnitude of $B$(in tesla) is :
(assume $g=9.8m{s}^{-2}$)

• A. $2$
• B. $1.5$
• C. $0.55$
• D. $0.65$

Answer 1

Answer: (D)

$0.65$

The wire is in equilibrium between force of gravity and force acting due to horizontal magnetic field.

Hence $mg=BIl$

$B=\frac{mg}{Il}$

$=\frac{0.2\times 9.8}{2\times 1.5}$

$=0.65T$