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Class 12 › Physics › Moving Charges and Magnetism
CBSE2019Class Class 12 · Physics2 Marks · Short✅ Verified
A horizontal wire 0.1 m long carries a current of 5 A. Find the magnitude and direction of the magnetic field which can support the weight of the wire. (Mass per unit length $= 3 \times 10^{-3}$ kg/m, $g = 10$ m/s$^2$)
✅ Answer & Solution
For the wire to be supported, magnetic force must balance gravity:
$$BIl = mg$$
where $m = 3 \times 10^{-3} \times 0.1 = 3 \times 10^{-4}$ kg
$$B = \frac{mg}{Il} = \frac{3 \times 10^{-4} \times 10}{5 \times 0.1} = \frac{3 \times 10^{-3}}{0.5} = 6 \times 10^{-3} \text{ T}$$
Direction: horizontal and perpendicular to the wire (so that $\vec{F} = I\vec{l} \times \vec{B}$ acts upward).
