Two insulated wires perpendicular to each other in the same plane carry currents

Question

Two insulated wires perpendicular to each other in the same plane carry currents as shown in the figure (Figure 1) . Assume that I = 13 A and d = 18 cm.

Find the magnitude of the net magnetic field these wires produce at points P and Q if the 10 A current is to the right. Express your answers using two significant figures separated by a comma.

Find the magnitude of the net magnetic field these wires produce at points P and Q if the 10 A current is to the left. Express your answer using two significant figures separated by a comma.

Explanation / Answer

You need to know that to find the direction of the magnetic field, point the thumb of your RIGHT hand in the direction of current flow. Ledt your fingers curl naturally. The tips of your fingers will point in the direction of the magnetic field.

A) Compute the field from each wire at point P individually and combine them together paying attention to whether the directions are the same (add them) or opposite (subtract them). Do the same for point Q.

B) The only thing that changes is the direction of one current so just do the opposite operation at each point.

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Using B = (mu/2pi) (I/r)

(2 x 10^-7) 13/.15 = 1.733 x 10^-5 T
and
(2 x 10^-7) 10/.08 = 2.50 x 10^-5

Adding for (a) to get 4.233 x 10^-5 (both fields out of the page)
Subtracting for (b) to get 0.767 x 10^-6 (stronger field into page)

Since it asks for the magnitude of the field, I don't believe a negative answer could be correct.

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