a wire with mass per unit length 75 g/m runs horizontally at right angles to a uniform horizontal 0.12 T magnetic field. what amount of current must flow through the wire for it to be suspended against gravity by magnetic force

The amount of current that must flow through the wire for it to be suspended against gravity by magnetic force = 6.125 A

Explanation:

Force on a wire carrying current in an electric field is given by

F = (B) (I) (L) sin θ

For this question,

The magnetic force must match the weight of the wire.

F = mg

mg = (B) (I) (L) sin θ

(m/L) g = (B) (I) sin θ

Mass per unit length = 75 g/m = 0.075 kg/m

B = magnetic field = 0.12 T

I = ?

g = acceleration due to gravity = 9.8 m/s

θ = angle between wire's current direction and magnetic field = 90°

0.075 * 9.8 = 0.12 * I sin 90°

I = 0.075 * 9.8/0.12 = 6.125 A