Answer:
a) The magnetic field should point upwards(i.e the north)
b) The magnitude of the weakest possible magnetic field is 0.681 Tesla
Explanation:
a) Since the force of gravity is acting vertically downwards, for equilibrium to be maintained, the force due to the magnetic field should act upwards in the north direction. since F = I (LXB), and the aim is to obtain a maximum LXB using the weakest possible magnetic field, according to the right hand rule, the magnetic field must point in the morth direction (i.e upwards) to maintain a balance between gravity and force due to magnetic field.
b) mass, m = 25.0g = 25 * 10⁻³kg
Length, L = 1.8m
Current, I = 6/30 A
g = 9.8 m/s²
F = mg................(1)
F = ILB................(2)
Equating (1) and (2)
mg = ILB
B = mg/IL
B = (25 * 10⁻³*9.8)/(6/30 * 1.8)
B = 0.245/0.36
B = 0.681 Tesla