Physics 2102 Jonathan Dowling Review Session Midterm 3 Checkpoints Questions Magnetic field Force on each wire due to currents in the other wires Magnitude of B ds The current in wires A B D is out of the page current in C is into the page Each wire produces a circular field line going through P and the direction of the magnetic field for each is given by the right hand rule So the circles centers in A B D are counterclockwise the circle centered at C is clockwise When you draw the arrows at the point P the fields from B and C are pointing in the same direction up and left A length of wire is formed into a closed circuit with radii a and b as shown in the Figure and carries a current i a What are the magnitude and direction of B at point P B 0 i 4 R b Find the magnetic dipole moment of the circuit NiA Induction and Inductance Faraday s law EMF d B dt or r r d B C E ds dt Inductance L N I For a solenoid L 0n2Al 0N2A l Inductors EL L di dt RL circuits i t E R 1 e tR L or i t i0e tR L Magnetic energy U Li2 2 u B2 2 0 i Checkpoints Questions Magnitude direction of induced current Magnitude direction of magnetic field inducing current Magnitude of induced emf current Given E ds direction of magnetic field Given B dB dt magnitude of electric field Current inducing EL Largest L Current through the battery Time for current to rise 50 of max value Largest current R L or 2R L or R 2L or 2R 2L When the switch is closed the inductor begins to get charged and the current is i E R 1 e tR L When the switch is opened the inductors begins to discharge The current in this case is then i E R e t2R L Maxwell s Equations Gauss E dA q 0 S nameless B dA 0 S d B ds 0 0 E dA 0i Ampere Maxwell s dt S C Displacement current d Faraday s E ds B dA C dt S Checkpoints Questions Given A B at top and bottom flux through curved sides Rank integration paths according to B ds B Magnetic field induced by E Is E increasing or decreasing Given a uniform E t in a circle magnetic field at the edge Discharging capacitor direction of displacement current magnetic field Charging capacitor Which curve is for the B in the wire which for B in the capacitor gap Map points a b c d into 1 2 3 A parallel plate capacitor has square plates 1 0 m on a side as in Fig 32 35 A current of 3 2 A charges the capacitor producing a uniform electric field E between the plates with E perpendicular to the plates a What is the displacement current through the region between the plates b What is dE dt in this region c What is the displacement current through the square dashed path between the plates d What is B ds around this square dashed path
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