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12.Parallelism.Three parallel wires carry the same currentI. Their positions and current di-rections from a cross-sectional view is shown. What is the net force on the rightmost wire?A.3μ0I24πd, to the rightB.3μ0I24πd, to the leftC.μ0I24πd, to the rightD.μ0I24πd, to the leftSolution:Since the currents of opposite direction repel, both the leftmost wire and themiddle wire will push the rightmost wireto the right. In magnitude, the net force ismu0I22πd+mu0I22π(2d)=3μ0I24πd.B – 6
Second Long ExamMidyear, AY 2015–2016Physics 7213.Wire inside a ring.An infinitely long straight wire carryingcurrentI1passes through the center of a circular loop of wirecarrying currentI2, as shown. The long wire is perpendicularto the plane of the loop.Which of the following is TRUEabout the magnetic force on the loop?Solution:heheB – 7
Second Long ExamMidyear, AY 2015–2016Physics 72For the next two items, consider a circular current loop of radius5.0 min theyzplane with a2.5 Acurrent as shown (the+x-axispoints out of the page).14.Sa Gitna.What is the magnitude of the magnetic field at thecenter of the loop?15.Feel mo ba?What is the direction of the magnetic field?16.Yakapin mo ako ng amperian loop.A currentIis distributed uniformly over the cross-sectional area of a cylinder of radiusR. A concentric circular amperian loop with radiusr < Rencloses a fraction of the cylinder’s current. Which of the following expressionsfollows from Ampere’s law and leads to the magnetic fieldBinside the cylinder?A.B(πr2) =μ0IR3r3B.B(πR2) =μ0Ir3R3C.B(2πr) =μ0Ir2R2D.B(2πR) =μ0Ir2R2
B – 8
Second Long ExamMidyear, AY 2015–2016Physics 72Solution:Enclosed current isIencl=ItotAtotAencl=IπR3(πr3)=Ir2R2.Using symmetry arguments,H~E·d~A, simplifies toE(πr2). So Gauss’s law becomesI~B·d~l=μ0Iencl-→B(2πr) =μ0Ir2R2B – 9