Exercise 5-4: A horizontal wire with a mass per unit
length of 0.2 kg/m carries a current of 4 A in the
+x direction. If the wire is placed in a uniform magnetic
flux density B, what should the direction and minimum
magnitude of B be in order to magnetically lift the wire
vertically upward? [Hint: The acceleration due to gravity
is g = −ˆz 9.8 m/s2
Answer: B = ˆy0.49 T.