EXAM 2               April 10, 1996            PHYS 208 Honors
	
	YOUR NAME:___________________________________________
	
	    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?  
	 
	
	
	
	   For the remaining problems, place the equations representing the
	physics principles you are using in the box on the page.  You may
	use an English label for the principle, the general form of the
	equation, or the form you get applying the principle to the problem
	at hand.  Each question counts 30 points.
	
	2. An electron enters a uniform magnetic field  B   at an angle
	           ->
	theta  to  B .  Determine the radius and pitch (distance between 
	loops) of the electrons's helical path, assuming its velocity  
	v  is known. 
	
	Diagram:
	
	
	
	
	
	
	
	
	
	
	Principles:
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	3.  Determine the current through each of the resistors in the figure
	below.
	
	
	Label diagram completely:
	
	      _____________________________________
	     |                  |                  |
	   __|__                |                __|__
	 _________ V            R             __________  V
	     |                  |                  |
	     |                  |                  |
	    2R            ______|_______          2R
	     |                _____       2V       |
	     |                  |                  |
	     |_______ R ________|_________ R ______|
	                                    
	                                                            
	
	The current in the center branch is  6V/(5R).  
	[Mark the printed diagram to show the currents you are defining. 
	This and the writing of a complete set of equations (assuming that
	you do *not* know the middle current) will get most of the credit
	for the problem.  If you get lost in algebra, move on to other
	problems and return if you have time. Justify your equations.]

	Equations assuming middle current not known:
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	4. (From homework)  A long, straight wire carries a current  I1 as
	shown in the figure below.  A rectangular coil with two sides
	parallel to the straight wire has sides of  a  and  b  with the near
	side a distance  c  from the wire.  The coil carries a current  I2. 
	Find the force on each segment of the coil and the net force on the
	coil as a whole.  Justify the formula you use for any magnetic fields.

	
	Diagram:
	
	   |            a
	   |      ____________
	   |     |            |
	   |     |            |
	   |     |            |
	   |     |            |
	   |     |            |   b
	   |     |            |
	   |     |            |
	   |     |            |
	   |     |____________|
	   |
	   |<--->
	      c
	
	Principles:
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	You can use this page to finish any of the problems that need more
	than one page to work.  Be sure to number the problems.