A loop of wire is in the shape of two concentric semicircles as shown. (Figure 1) The inner circle has radius a; the outer circle has radius b. A current I flows clockwise through the outer wire and counterclockwise through the inner wire. What is the direction of the magnetic field at the center of the semicircles?

Question 4 A loop of wire is in the shape of two concentric semicircles as shown. (Figure 1) The inner circle has radius a; the outer circle has radius b. A current I flows clockwise through the outer wire and counterclockwise through the inner wire. Figure 1 of 1 a Part A What is the magnitude, B, of the magnetic field at the center of the semicircles? Express B in terms of any or all of the following: I, a, b, and H. H01 (1- 40 B = Ho Submit Hints My Answers Give Up Review Part Correct To see whether B~ 1/a and B~ 1/b makes sense, think of the scaling of different quantities. The size of the current element scales as the radius, whereas the power of in the denominator is 2 (and equals the radius also, in this case). So over all, you would expect the magnetic field to scale as 1/radius. Note that such an argument works only because the field due to each point is in the same direction, so you are doing a much simpler integral. Part B What is the direction of the magnetic field at the center of the semicircles? into the screen out of the screen Submit My Answers Give Up Provide Feedback Continue