Download Physics 224

Physics 224 - Test #2
March 2, 2009
Name___________________________________________________
Total Problem 1: _____________/25
Total Problem 2: _____________/25
Total Problem 3: _____________/25
Total Problem 4: _____________/25
Total Problem 5: _____________/25
Total Problem 6: _____________/25
Total Points:__________________________/125
Percentage Score: ______________________
%
***You will answer only 5 of the 6 problems for exam credit; your choice. All problems require you to
show all the steps in obtaining the answer or to provide clear and complete descriptions/explanations.
This includes, but is not limited to, defining all variables, showing the equations to be used, explaining
a concept and including units with all values listed. All problems are worth up to 25 points each.
Good Luck!!!!
**In addition, the sixth problem may be completed for extra credit! Please
be sure to indicate which one of the problems you're using for extra
credit.....otherwise the five lowest scored problems will be used to
determine your grade and you will NOT receive extra credit for the
remaining problem!!
1) Shown below is a DC circuit that contains two switches. Each switch is resistance-less when
closed. All of the connecting wires should be considered to have zero resistance. All of the resistors
shown are identical. The circuit contains an ideal ammeter (A) used to measure the current in the
circuit. The diagram shows the switches open. Below the diagram are four different switch
configurations for the circuit.
Of the switch configurations shown, which one will
produce the largest reading on the ammeter?
2) The following diagrams show three separate
situations involving charges on metal spheres
that are initially in contact. The positively
charged rod is brought up to the same
distance from each set of metal spheres. The
spheres are then separated simultaneously
from each other using the insulating handles.
Finally the charged rod is removed. After the
rod is removed which rank the spheres from
most positive to most negative?
3) The capacitor in the figure has a crosssectional area Ao and a distance between plates
y. The thickness of each metal plate is t.
A battery with voltage Vo is connected across
the plates of the capacitor. There is nothing
between the plates of the capacitor. For each
modification listed below, state whether the
capacitance increases, decreases, or remains
the same.
Modification
1. Increase the distance y
2. Increase the area Ao
3. Increase the plate thickness t
4. Insert a dielectric material between the plates
5. Increase the battery voltage Vo
Effect on capacitance
Increases Decreases Remains Same
4) Two equal and opposite charges are fixed in space at
the locations shown. Seven points are labeled A - G in the
vicinity of these charges.
For each pair of points, decide whether the electric
potential at point 1 is greater than, less than, or equal to
the electric potential at point 2. Assume that the electric
potential is zero far away from the charges.
Point 1
Point 2
A
C
A
B
A
D
A
F
A
E
B
C
B
D
B
E
F
G
D
E
Electric Potential
(> or < or =)
Explanation
5) In each case below, small charged particles are fixed on grids having the same spacing. Each
charge q is identical, and all other charges have a magnitude that is an integer multiple of Q. Rank
the magnitude of the force on the charge labeled q due to the other charge(s) in its grid. Be sure to
illustrate the force vector(s) on q as part of your explanation.
6) Using loop and junction rules only, list all the possible associated current and voltage equations
related to the figure below.
BONUS: If both batteries are 1 V and all of the resistors are 1 W. What are the unknown currents in
the problem above?