Reply quickly, quiz in a few hours, very simple magnetic field question

1. Aug 2, 2008

WardenOfTheMint

1. The problem statement, all variables and given/known data

At a certain location, Earth has a magnetic field of 0.70 10-4 T, pointing 75° below the horizontal in a north-south plane. A 8.5 m long straight wire carries a 12 A current.
(a) If the current is directed horizontally toward the east, what are the magnitude and direction of the magnetic force on the wire?
Magnitude
N
Direction

horizontal and directed due west
15° above the horizontal in the northward direction
15° below the horizontal in the southward direction
75° below the horizontal in the southward direction
75° above the horizontal in the northward direction
horizontal and directed due east

2. Relevant equations

(Force) = (BsinΘ)(I)(L)

In English...(magnetic force) = (magnetic field perpendicular to current)(current)(length)

3. The attempt at a solution

I know the answer, it is...
F = (0.70 10-4 sin 90) (12 ) (8.5) = (7.14 e -3) N
15° above the horizontal in the northward direction

But I don't understand that the ( ' sin 90 ' ) bit. The magnetic field is 75° below the horizontal and the current is directly on the horizontal. So shouldn't it be sin 75°? I don't understand how can I apply the right hand rule 1 to this situation?

I don't understand what the question is asking, is the magnetic field going into the page (if so, then the force being 15° above the horizontal makes sense).

2. Aug 2, 2008