A long straight wire of length $2 \mathrm{~m}$ and mass $250 \mathrm{~g}$ is suspended horizontally in a uniform horizontal magnetic field of $0.7 \mathrm{~T}$. The amount of current flowing through the wire will be $\left(g=9.8 \mathrm{~ms}^{-2}\right)$

• A

  $2.75 \mathrm{~A}$
• Correct answer
  B

  $1.75 \mathrm{~A}$
• C

  $2.45 \mathrm{~A}$
• D

  $2.25 \mathrm{~A}$

Solution

we know $\begin{aligned} & F=m g \\ & I \ell B=m g\end{aligned}$ $I=\frac{m g}{\ell B}=\frac{250 \times 10^{-3} \times 9.8}{(2)(0.7)}$ $\begin{aligned} & I=1750 \times 10^{-3} \mathrm{~A} \\ & I=1.75 \mathrm{~A}\end{aligned}$

Hence, the correct answer is option: 'B'.