Lectures_Lect16

Lectures_Lect16 - Physics 212 Lecture 16, Slide Physics 212...

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Unformatted text preview: Physics 212 Lecture 16, Slide Physics 212 Lecture 16, Slide 1 Physics 212 Physics 212 Lecture 16 Lecture 16 Motional EMF Induced emf !! Induced emf !! Conductors moving in B field Conductors moving in B field Physics 212 Lecture 16, Slide Physics 212 Lecture 16, Slide 2 The Big Idea When a conductor moves through a region containg a magnetic field: Magnetic forces may be exerted on the charge carriers in the conductor 05 v v These forces produce a charge separation in the conductor X X X X X X X X X X X X X X X X X X B B X X X X X X X X X X X X X X X X X X +- F F This charge distribution creates an electric field in the conductor The equilibrium distribution is reached when the forces from the electric and magnetic fields cancel The equilibrium electric field produces a potential difference (emf) in the conductor B v q F × = +- +- E +- E + F B F E qE qvB = vB E = EL V = L L vBL V = Physics 212 Lecture 16, Slide Physics 212 Lecture 16, Slide 3 Rotate picture by 90 Rotate picture by 90 o (top view) (top view) v v X X X X X X X X X X X X X X X X X X B B X X X X X X X X X X X X X X X X X X X X v v b a :22 Bar a Bar a No force on charges No charge separation No E field No emf Checkpoint 1 A B C D +- F F a = 0 = 0 +- F F F F b = qvB = qvB Bar b Bar b Opposite forces on charges Charge separation E = vB emf = EL = vBL Two identical conducting bars (shown in end view) are moving through a vertical magnetic field. Bar (a) is moving vertically and bar (b) is moving horizontally. Which of the following is true? A. A motional emf exists in the bar for case (a), but not (b) B. A motional emf exists in the bar for case (b), but not (a) C. A motional emf exists in the bar for both cases (a) and (b) D. A motional emf exists in the bar for neither case (a) nor case (b) B Physics 212 Lecture 16, Slide Physics 212 Lecture 16, Slide 4 :22 Rotate picture by 90 Rotate picture by 90 o A B C D v v X X X X X X X X X X X X X X X X X X B B X X X X X X X X X X X X X X X X X X +- F F F F b = qv = qv B B Bar Bar Opposite forces on charges Charge separation E = v B emf = EL = v BL Checkpoint 2a A B V R I Equivalent circuit Equivalent circuit Changing Area A conducting bar (green) rests on two frictionless wires connected by a resistor as shown. The entire apparatus is placed in a uniform magnetic field pointing into the screen, and the bar is given an initial velocity to the right....
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Lectures_Lect16 - Physics 212 Lecture 16, Slide Physics 212...

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