Phys 313 Quiz 10

Question 1

The electric potential at distance r from a point charge Q is

          ke * Q              Q
      a.  ------     b. -------------    c. a and b     d. neither a nor b
           r^2          4 pi eps0 r^2

   Answer:  It is neither a nor b -- actually, the potential is

                            ke * Q                                   
                V(r)  =   ----------
                               r

Question 2

A charge Q = +1 is at x = 0. A charge Q = -1 is at x = 1. Should the electric potential at point P, x = 2, be positive, negative, or zero?


   Answer:    The electric potential at P will be negative.

Question 3

Hydrogen atoms contain 1 proton and 1 electron. To separate the particles by 1 meter requires

   a. positive work done on the atom
   b. negative work done on the atom

   Answer:  Positive work done on the atom.  As one moves them apart,
            an attractive force tries to pull them back together.
            The person pulling them apart does positive work (spends energy)
            on the atom.  The electric force does negative work
            (stores it up as electric potential energy).