PY212 Solutions Quiz 7(a) There is a current because of the emf and the resistance: Ri/ε=(this is Ohm’s law). The emf is produced by a change in flux which is produced by a change in area (see also Eq. 30-8): V,14.0)m/s25)(m100.8)(T1070()()()1(23=××=====Φ=−−BLvdtdxBLdtLxdBdtBAddtdNεsuch that mA.8.2)50/()V14.0(/=Ω==Riε(b) There are two ways to find the direction of the current (both using Lenz’s law): •“Nature is working against us”; it produces a force opposite to our force. We are pulling the rod to the right, so the induced force (which is caused by the induced current) is to the left. The right-hand rule tells us that the current must be going up(because Bis into the page and the induced force is to the left). •“Nature tries to fix the magnetic flux.” In this case the flux is becoming smaller, so Nature induces a magnetic field Bindto try to fix the flux. We are making the flux smaller, so Nature tries to make it larger; in other words Bindis directed into
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