Q. A straight wire of mass $300 ,g$ and length $ 2.5text{ }m $ carries a current of $ 3.5text{ }A $ . It is suspended in mid-air by a uniform horizontal magnetic field $B$. What is the magnitude of the magnetic field?

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A straight wire of mass $300 ,g$ and length $ 2.5text{ }m $ carries a current of $ 3.5text{ }A $ . It is suspended in mid-air by a uniform horizontal magnetic field $B$. What is the magnitude of the magnetic field?

Solution:

Here weight of the wire is balanced by the extene magnetic force.

So, $ Bil=mg $

$ B=frac{mg}{il} $

$ =frac{300times {{10}^{-3}}times 10}{35times 2.5}=0.34,T $