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18.Tatluhan.Consider 3 infinitely long current-carryingwires as shown. What is the direction of the magneticforce experienced by wire Z due to wires X and Y?A. to the rightB. to the leftC. upwardsD. downwardsSolution:Force on C due to A: upwardsForce on C due to B: downwardsFor an infinitely long wire, magnetic field is:B=μ0I2πRB is closer to CFor the next four items, consider a rectangular loop in a uni-form constant magnetic field as shown.19.Tick.Which of the following will produce aclockwisecurrent in the loop?I. Increasing the magnitude ofB.II. Increasing the lengthbof the loop.III. Rotating the loop counterclockwise about an axisparallel toB.20.Pinsan.If only the widthachanges asa(t) =acos(ωt)whileBis constant, what is theemf induced in the loop att=π2ω?A – 9
Second Long ExamFirst Semester, AY 2014–2015Physics 72ave=-ΔΦBΔt=-0-Babπ/2ω= 2Babω/π21.Bagsakin.If the the magnitude of the magnetic field fluctuates asB(t) =B0+δsin(ωt)for fixedaandb, how would the induced emf change with time?=-dΦBdt=-ddtab[B+B0sin(ωt)] =-B0ab[ωcos(ωt)] =-B0abωcos(ωt)22.Tock.If the lengthbincreases asb(t) =b+βt(β >0), what would be the directions ofthe induced emf and induced current?A. Both clockwiseB. Both counterclockwiseC. Clockwise emf, counterclockwise currentD. Counterclockwise emf, clockwise currentSolution:Flux is increasing, so the induced emf and induced current will oppose thischange.R.For the next two items, consider a thin conducting rod oflengthLriding along two parallel conducting rails withconstant velocityvas shown. The rails and the rod, bothwith negligible resistance, are connected to a resistor23.EMotional UP.If the system is immersed in a uniform constant magnetic fieldBdirectedupward, what is the induced emf produced between the rod?A – 10
Second Long ExamFirst Semester, AY 2014–2015Physics 7224.EMotional INTO.If the system is immersed in a uniform constant magnetic fieldBdi-rected into the page, what is the induced current passing through the resistor?√32vBLRvBLR√32vBLThus, induced current is√32vBLR.