EXAM 2                    October 29, 1992                 PS 208

    If you need a constant not given here or do not understand                 
                                                                               
a problem, please ask me about it.  No notes, books, etc. may                  
                                                                               
be used during this exam.                                                      
                                                                              
                 2                                -19                         
    g = 9.8 m/sec                     e = 1.6 x 10    C                        
                                                                               
                                 9    2    2                                   
     1/(4 pi epsilon ) = 9.1 x 10  N m  / C                                    
                    0                                                          
                                                                               
                      -7                                                       
     mu  / (4 pi) = 10   T m/ A                                                
       0                                                                       
                                                                               
                                           -31                                 
     The mass of the electron is 9.11 x 10     kg.                             
                                                                               
 1.  (10 points) 

      (a).  Explain the relationships among Force, Electric Field, 

Potential Energy, and Electric Potential.  

      (b). How can you use these relationships to remember the formula 

giving the Electric Potential when the Electric Field is known and the 

formula for the Electric Field when the Electric Potential is known?  
 

 2.  (30 points) 
      Find  the effective capacitance of N capacitors with capacitance 

C  ... C  connected in series.
 1      N
   

 3.  (30 points) [From lecture]

      (a)  What is the potential difference between the plates of a 

cylindrical capacitor of length  L  carrying a charge  Q  on each plate.  

The radii of the inside and outside cylinders are  R  and  R  
                                                    1       2
respectively, and there is a dielectric of dielectric constant  kappa  

between the plates.

      (b)  What is the capacitance of this capacitor?
 

 4.  (30 points) [From homework]

     A circular coil of diameter  d  and containing  N  loops lies flat 
                                                                ->
on the ground.  The earth's magnetic field at this location is  B  ; it 

points into the earth at an angle  theta  below a line pointing due north.  

If a current  I   passes clockwise through the coil [i.e. in the 

direction that the hands of a watch would move if the watch were face-

up on the ground], 

      (a) determine the torque on the coil; 

      (b) show which edge (north, south, east, or west) tends to rise.