The point P lies along the perpendicular bisector of the line connecting two long straight wires S and T perpendicular to the page. A set of directions A through H is shown next to the diagram. When the two equal currents in the wires are directed into the page, the direction of the magnetic field at P is closest to the direction of
A)E.
B)F.
C)G.
D)H.
E)A.

Question

The point P lies along the perpendicular bisector of the line connecting two long straight wires S and T perpendicular to the page. A set of directions A through H is shown next to the diagram. When the two equal currents in the wires are directed into the page, the direction of the magnetic field at P is closest to the direction of 
A)E. 
B)F. 
C)G. 
D)H. 
E)A.

Quizplus · Accepted Answer

By the right-hand rule, the magnetic field at P will be perpendicular to the plane of the page and pointing out of the page. Using the right-hand rule again, we see that the magnetic field due to each wire will be pointing in opposite directions along line PT, so they will cancel each other out at point P. Therefore, we need to choose a direction that is perpendicular to line PT and pointing out of the page, which is direction E.

The Point P Lies Along the Perpendicular Bisector of the Line