Question

A horizontal metal bar oriented east-west drops straight down in a location where the earth's magnetic field is due north. as a result, an emf develops between the ends. which end is positively charged?

Answer 1

Metal bar is aligned along East- West direction and it is dropped vertically down

So its velocity is along -Z direction,

Now the Earth's magnetic field is towards north so its towards +Y direction

now we have formula for force on a moving charge

$F = q(v X B)$

v = - z direction

B = + y direction

now by the above formula

$F = q(v(-k) X B(j))$

$F = qvB (i)$

So force is towards East

so all positive charge is towards East end