Updated:  8/23/04
                  
           Chapter 16    Electric Charge and Electric Field  

          A. Instruction to students:
                          Homework:
                          1.) Read carefully all sections.
                          2.) Do Examples 16-1,2,3 and 16-5,6,7
                          3.) All multiple problems posted
                                                 

          B. Biomedical (and technological) application:
                          Electric forces in molecular biology: DNA structure and replication.  
                          In text: Section 16-10;   pp493-495.

 
          C. Lectures and study guideline
 
          The force
          Unlike charges attract and like charges repel.  
          The force F between two charges Q1 and Q2 separated by a distance r is given by Coulomb's
           law,
                                      F               = (9.0 x 10^9 N m^2/C^2) Q1*Q2/r^2
                          such as
                              1.0 x 10^(-3) N  = (9.0 x 10^9 N m^2/c^2) [10^(-6) C] x [10^(-6) C] / (3 m)^2.
                          That, is the force between two charges of a microcoulomb each at 3 m separation is
                          0.01 N.  (10^(-6) = micro, and 10^(-9) = nano, etc.  See "Metric (SI) Multipliers"
                          on the second page following the cover of the text.)
                
               Simple questions:
                1)  When the distance between the two charges is doubled, how the force between the two
                      changes?
                     How about when the distance is tripled?
                2)  Illustrate the force "between" the two charges when the charges positive.  Your
                     illustration is an example of one of Newton's law.  Which one is it?   Repeat for the case
                     that one charge is posirive and the other negative.

          The smallest charge in the universe  
          No charge smaller than (the magnitudes of ) those of electrons and protons has been observed. 
          The smallest unit is
                                  e = 1.6 x 10^(-19) C.
                Simple question:
                 1) How many electrons make 1 C.
              

           Electric field
           Read pp490-92 carefully to understand how to draw the electric field lines shown in
           Figs. 16-26 through -32.
                Simple questions:
                 1) Do electric field lines exist?
                 2) Do electric fields exist?   If they do, how can you show they do?