A wire carries current in the plane of this paper toward the top of the page. The wire experiences a ma netic force toward the right edge of the page. The direction of the magnetic field causing this force is: A. in the plane of the page and toward the left edge
B. in the plane of the page and toward the bottom edge
C. upward out of the page
D. downward into the page

D) True. In this case the thumb goes up the page, the fingers are extended out of the page and the palm points to the left

Explanation:

The magnetic force on a conductor is given by

        F = i L x B

bold letters indicate vectors. We can write this expression in the form of magnitudes

         F = i L B sin θ

The direction of the force can be found by the rule of the right hand, the thumb points in the direction of the current, the fingers extended in the direction of the magnetic field and the palm gives the direction of the force

Let's apply this expression to the case presented.

A) False. In this case the force is out of the page and is in contradiction with the real force

B) False. In this case the force is zero since the displacement of the current and the field would be parallel

C) False. In this case the force is to the left

D) True. In this case the thumb goes up the page, the fingers are extended out of the page and the palm points to the left

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