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Fall 2012 Midterm 3 Solutions

# T0 is the moment you release the rod from rest note

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Unformatted text preview: he moment you release the rod from rest). (Note, the bar is sliding on frictionless rails). Initially, there is no motional emf because there is no motion, so acceleration depends on battery voltage, resistance, magnetic field, and mass of the rod. Doubling R cuts initial acceleration in half. A) B) C) D) E) vt is half and a0 half vt is twice and a0 twice vt is half and a0 is the same vt is the same and a0 half vt is the same and a0 is the same Terminal velocity occurs when the motional emf cancels the battery emf and reduces the current (and hence the magnetic force) to zero. Since current is zero at terminal velocity the resistance is irrelevant. Version 1 Page 5 10. The solid circle of radius R in the diagram shows the cross section of a long solenoid with its axis pointing straight into the page. The current in the solenoid is increasing steadily. The dashed concentric circles are four integration paths in a plane perpendicular to the solenoid axis that have radii of r1 = R/4, r2 = R/2, r3 =2R, and r4 = 3R. Rank the paths according to the magnitude of the circulation of the electric field, E dl along each path, least to greatest. R 1 A) B) C) D) E) 2 3 4 The circulation is the integral on the left side of Faraday's law (as defined in the problem). Basically, you need to compare the circulations by looking at the right side of Faraday's law. Path 3 and 4 tie because there is no flux outside the solenoid and they both surround all of the flux inside. Path 2 is larger than pat...
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