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Transcript
Motional EMF Motional emf • e = BLv – B: magnetic field (T) – L: length of bar moving through field – v: speed of bar moving through field. • Bar must be “cutting through” field lines. It cannot be moving parallel to the field. • This formula is easily derivable from Faraday’s Law of Induction Motional emf - derivation • • • • • e = DFB/Dt e = D(BA) /Dt (assume cosq = 1) e = D(BLx) /Dt e = BLDx /Dt e = BLv Sample Problem • How much current flows through the resistor? How much power is dissipated by the resistor? 3 W 50 cm B = 0.15 T v = 2m/s Sample Problem • In which direction is the induced current through the resistor (up or down)? 3 W 50 cm B = 0.15 T v = 2m/s Sample Problem • Assume the rod is being pulled so that it is traveling at a constant 2 m/s. How much force must be applied to keep it moving at this constant speed? 3 W 50 cm B = 0.15 T v = 2m/s Lab: Magnetic Field Map Using a compass, map the magnetic field inside and outside your solenoid. Do the following: a) Put together 4 sheets of graph paper. Write all group members’ names on paper. b) Trace the solenoid (true size) I c) Draw the Compass Rose d) Connect to DC outlet e) Map magnetic field lines with compass f) Draw North and South Poles of solenoid g) Extend field lines through solenoid.