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A.2.00 AB.5.00 AC.10.0 AD.20.0 ASolution:B=μ0I2πdfor a current-carrying infinite wire. Thus,I=2πdBμ0= 10.0 A12.Equilateral Triangle.Consider three infinite currentcarrying wires shown.The wires, carrying the sameamount of currentI0, are each separated by a distances. If the field point P is at the midpoint of wires A andC, what is themagnitudeof the magnetic field strengthat P?A.2μ0I0πs+μ0I0√3πsB.μ0I0√3πsC.2μ0I0πsD.2μ0I0πs-μ0I0√3πsA – 6
Second Long ExamFirst Semester, AY 2014–2015Physics 72Solution:A and C cancel out. B only contributes.13.Infinite Wires.Which of the following figures correctly shows the current direction on aninfinite wire, and the corresponding magnetic field direction at the indicated field point?Solution:ANSWER: DA.μ0I04πRdθˆkB.μ0I04πRdθˆC.-μ0I04πRdθˆD.-μ0I04πRdθˆkSolution:Note thatds×ˆris directed into the page, i.e. to the-ˆj-direction. Also, notethatdsandˆrare perpendicular with each other. Using Biot-Savart law, we obtain C.14.Current Loop.An infinitesimal current element, sub-tending an angledθ, is located at some angleθon thecurrent-carrying circular loop shown. The loop is cen-tered at the origin. Which of the following is the correctexpression for the magnetic field contribution at the ori-gin, due to this element?A – 7
Second Long ExamFirst Semester, AY 2014–2015Physics 7215.BeeDiEl.Shown are 3 integration paths (X, Y, Z) with enclosed currents shown. What isthe correct order ofRB·dl?Note the magnetic field direction and integration path direction.For the next two items, consider a circular current loop ofradius5.0 min theyzplane with a2.5 Acurrent as shown.16.Sa Gitna.What is the magnitude and direction of themagnetic field at the center of the loop?17.Feel mo ba?What is the direction of the magnetic force experienced by anelectronmoving in the+xdirection as it enters the center of the loop?A – 8
Second Long ExamFirst Semester, AY 2014–2015Physics 72