If a straight wire of length 175 cm and mass 250 gm is suspended freely in a uniform horizontal magnetic field of 0.7 T, then the current flowing through the wire is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2 A
The wire hangs freely when the magnetic force \( BIL \) acting upward on it balances its weight \( mg \) (the wire is perpendicular to the horizontal field).
\( \displaystyle B I L = m g \;\Rightarrow\; I = \frac{m g}{B L} \)
\( m = 250\,\mathrm{g} = 0.25\,\mathrm{kg} \)
\( L = 175\,\mathrm{cm} = 1.75\,\mathrm{m} \)
\( g = 9.8\,\mathrm{m\,s^{-2}} \)
\( \displaystyle I = \frac{0.25 \times 9.8}{0.7 \times 1.75} = \frac{2.45}{1.225} = 2\,\mathrm{A} \)