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7.10 Recall the machined copper from last class, with steady current flowing left to right through it I I In steady state, do you expect there will be any surface charge accumulated anywhere on the walls of the conductor? A) Yes B) No © University of Colorado, 2011 7.1 Electricity and Magnetism II Griffiths Chapter 7 Maxwell’s Equations Clicker Questions 7.2 In the interior of a metal in static equilibrium the charge density ρ is: A) zero always B) never zero. C) sometimes zero, sometime non-zero, depending on the conditions. 7.3 Which of the following is a correct statement Charge Conservation of charge conservation? A) dQenclosed = - J · d l ò dt C) dQ enclosed B) = - òò J · dA dt D) E) None of these, or more than one. 7.4 For everyday currents in home electronics and wires, which answer is the order of magnitude of the instantaneous speed of the electrons in the wire? A. B. C. D. E. more than km/s m/s mm/s μm/s nm/s 7.5 An electric current I flows along a copper wire (low resistivity) into a resistor made of carbon (high resistivity) then back into another copper wire. In which material is the electric field largest? I A. B. C. D. In the copper wire In the carbon resistor It’s the same in both copper and carbon It depends on the sizes of the copper and carbon 7.6 A copper cylinder is machined to have the following shape. The ends are connected to a battery so that a current flows through the copper. A B C Rank order (from greatest to smallest, e.g. A=C>B) Magnitude of E field Conductivity Current Current Density © University of Colorado, 2011 7.7 Inside this resistor setup, what can you conclude about the current density J near the side walls? V=0 V0 I J?? I A) Must be exactly parallel to the wall B) Must be exactly perpendicular to the wall C) Could have a mix of parallel and perp components D) No obvious way to decide!?