1. Motional EMF

2. Motional emf  = 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

3. Motional emf - derivation  =  B /  t  =  (BA)  /  t (assume cos  = 1)  =  (BLx)  /  t  = BL  x  /  t  = BLv

4. Sample Problem How much current flows through the resistor? How much power is dissipated by the resistor?       B = 0.15 T v = 2 m/s 50 cm 3 

5. Sample Problem In which direction is the induced current through the resistor (up or down)?       B = 0.15 T v = 2 m/s 50 cm 3 

6. 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?       B = 0.15 T v = 2 m/s 50 cm 3 

7. Lab: Magnetic Field Map I 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) 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.