Review for Test 2


Here are some problems from last years exams:




1.(2pts each)


a)  T     F          Electrons tend to move uphill in potential.         


b)  T    F          A charge moving along an equipotential will not experience a change of

                        potential energy.


c)  T     F          Electric field lines are orthogonal to equipotential lines.


d)  T    F          When a positive charge moves along the Electric field lines its Kinetic

                        Energy decreases.


e)  T     F          In a parallel plate capacitor, the capacitance is independent of the material

                        between the plates.


f)  T     F          The plates of a parallel plate capacitor have an area of .004 square meters and

                        are separated by a distance of .2mm so the capacitance is 177 pF.


g)  T     F          Current is defined to be the amount of charge that flows.


h)  T     F          Resistivity is proportional to conductivity.


i)   T     F          If the charge on the plates of a capacitor doubles when a dielectric is placed

                        between the plates, the dielectric constant is k = 2.


j)  T     F          The direction of a current is the same as the flow of the electrons.




1.(2pts each) Note: Some are fill in the blank.


a)  T     F          The source that converts some form of energy into electrostatic potential

                        energy is a source of emf.         


b)  T    F          A real source of emf has no internal resistance.


c)                      __________ loop rule: The algebraic sum of the changes in potential around a  closed loop is zero


d)                     The __________ is the time needed for the charge on a capacitor to drop to 50%

                        of its initial value.


e)  T     F          No one has ever found a magnetic monopole.


f)                      If a proton is traveling from left to right across this page and a magnetic field

                        is projecting out from the page, the force acting on the proton would point

                        straight __________.


g)                     The net force on a current loop in a uniform magnetic field is ____________.


h)                     _____________


i)   T     F          The torque experienced by a current-carrying coil in a magnetic field is used

                        in motors.


j)  T     F          Ohmís law relates current and capacitance.




5.)(10pts)  Find the equivalent capacitance of the figure:


         2mF      3mF








6.)a)(5pts) A 2mF parallel plate capacitor is connected to a 9V battery.  A dielectric slab with a dielectric constant of 5 is inserted to fill the space between the plates.  Find the additional charge that flows to the plates.










b)(5pts)   When 12V is applied across a wire of length 200cm and radius 1mm, a current of 3mA flows through the wire.  Find the resistivity of the material.





7.)(10pts) A toaster operates at 120V with a current of 8A.  It takes 45sec to toast a slice of bread.  At 8 cents per kilo-watt-hour, what does it cost to toast a slice of bread?








4.a)(7pts)  A 2-mF capacitor is connected in parallel with a battery and a resistor.  When the battery is disconnected the charge on the capacitor falls to 37% of its initial value in 3 ms.  What is the resistance.









b)(8pts) In an RC charging circuit, R = 1000W, and C = 5-mF.  How long will it take to charge the capacitor to 80% of its final value?