### Exam 2 Solutions

```Physics 2220
Fall 2014
Dr. Tabitha Buehler
i
Name:
Exam 2
Unid:
Discussion TA:
SHOW ALL WORK!
1.
A capacitor is formed of two 1 mm thick parallel plates that are
separated by 2 mm. An identical metal plate is then carefully
inserted between the two plates so that a space of 0.5 mm is left
on either side of the new plate, as shown in the figure.
A.
B.
1 mm
31 mm
2 mm
13 1 mm
[6 pts.J Does the capacitance of the capacitor change after the metal plate is inserted between the two
original plates? Does it increase, decrease, or stay the same?
/6 pts.J Explain why a change does or does not occur.
,.
Co
"~
~~J
^~
Three capacitors are connected as shown in the figure. The capacitances
shown are as follows: Ci = 4 uF, C2 = 3 uF, and C3 = 5 uF. The battery
voltage is 6 V.
Ct
=-
A.
B.
[11 pts.J What is the magnitude of the charge on capacitor C2?
[11 pts.J What is the potential difference across the plates of
capacitor C3?
«*
Ci
C3
Spring 2014
Physics 2220
Dr. Tabitha Buehler
Name:
Exam 2
Unid:
Discussion TA:
2
SHOW ALL WORK!
The figure applies to the following three problems.
A.
B.
C.
50 u
[11 pts.J With the switch open, what is the current Ij? (A positive sign
means that current flows in the direction of the arrow.)
[11 pts.J How much current passes through the switch after it is closed?
[11 pts.J With the switch closed, what is the voltage difference,
V(A)-V(B)?
I>
SQ
,SQ
|L—^A/V---
IOSL
^ B
-AAAA-
-f
/c?v
6V
~4n
lov
Phsics 2220
Spring 2014
Dr. Tabitha Buehler
C
yfi)
Name:
3
Unid:
Discussion TA:
SHOW ALL WORK!
The switches Si and 82 in the figure are initially open (as shown), and the capacitors are initially uncharged. Then, at time
/ = 0, both switches are closed. Assume VB = 18 V, R, = 10 Q, R2 = 20 Q, R, = 30 Q, C, = 10 up, C2 = 20 uF, and
ft
A.
B.
C.
[11 pts.J What is the current through the resistor RI
immediately after the switches are closed?
[11 pts.J What is the current through resistor R2 a very
long time after the switches are closed?
[11 pts.J What is the charge on the capacitor €2 a very
long time after the switches are closed?
^\AA
Ci
*3
```