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.