General Physics II (PHYS 104)
Exam 2: March 30'2012
Name:
Multiple Choice (4 points each): Clearly circle the response (or responses) that provides the best
*rr"., to the followlng 12 questions. If you desire, neatly and briefly show any calculations or
reasoning off to the side. This work may be considered in the evaluation of the exam'
across a 100 V battery. After the battery fu1ly charges the
' A 6.0 pF air capacitor is connected
oil (dielectric constant rc : 4.5). How much
1)
capaciior, the capacitor is immersed in transformer
additional charge flows from the battery, which remained connected during the process?
-U
I
a) 1.2 mC
u
Q:qrav '
=
{'- X
1:: 7!i v' :--
ii
(-'
'(-''
i./
r ':f,(r Art : {,i- I'r,S-[, 1t:i'l' : i"7/"'
,
d) 2.5 mC
l\0
'r= C{ i-
Ci
-' *l"n
.xi
'(
t'--l"(.
2) A dielectric material such as paper is placed between the plates of a capacitor holding a fixed
charge. What happens to the electric field between the plates?
a) No change.
ci'
I
b) Becomes stronger.
It
weaker.
@ B".o-es
AVt\1
d) Reduces to zero.
fl,-.--
'-
I
+0'5
3) Four point charges are positioned on the rim of a circle. The charge on each of the four is
to
pC, +1.5 pC, -1.0 LrC, uttd -0.S pC. If the electrical potential at the center of the circle due the
-a,K
four charges?
a)0
x,.101
V
,
-!)._9.0
[c) 4.5 x 10.-V
d) -4.5 x 10* V
e)
18.0
x
10a
;.
-=
\1 ir u Ll.'
vi+ ' B i 'D
'--
I -l i.
, t.. tic
1v.rj
V
I
Qg=
*,{"4(
.i
a) It remains the same.
b) It is doubled.
ttecreases by a factor of 2.
d) It decreases by afactot of 4.
e) It increases by a factor of4.
i\
I /-j!
fL\t)
( -f:_
i'
\r*
Lvuj -' t
i-
4) Apara\lel-plate capacitor is connected to a battery. What happens to the stor_ed energy if the
piateseparationisdoubledwhilethecapacitorremainsc@?
l:
u\
5) A 12-V battery maintains the electrical potential difference between two parallel metal plates
separated by 10 cm. What is the electric field between the plates?
a)I.ZYlm
ly:*,trn(i
b) 12Ylm
#rav=ay'
t)-l?9sl d) z.ero , _, ,/
f* = - # * #r,
% lap v/rn
6) The electric potential at a certain point is space is 12 V. What is the electric potential energy
of a -3.0 pC charge placed at that point?
b) -4 x 10-6J
c) +36 x 10-6J
e) zerox 10-6J
F*-M
i*f:
r:" '$ ,'f.t *-1r'!
*34
-3 4( lev =
xldd
f
7) When a light bulb is connected to a 4.5 V battery, a current of 0.16 A passes through the bulb
filament. What is the resistance of the filament?
J* H*!#
Ft
ffim
Q=
r\ N
-t'
q,Tv
=
,16 ft
-k-d
8)
A coffee maker, which draws 13.5 A of current, has been left on
charge passes through the coffee maker during that time?
a) 0.0225
r_ .ry",
b) 1.35
*J* -::r *'*H"
C
for
10 minutes.
How much
#
C
.d"\i-.Lrr
d-hi:;i
1$
T Af
:
\g'5
f foo, = 8lc0 c
9) How does the resistance of a piece of conducting wire change
are doubled?
a) Remains the same
b) 2 times as much
c) 4 times as much
ld)
t-\
.-l
e)
f
%asmuch
7q ZS
fir].]Clf
I
if both its length and diameter
The sketch shows cross sections of equipotential surfaces between two charged conductors
shown in solid black. Points on the equipotentiai surfaces near the conductors are labeled A, B,
c, ..., H.
10.
!trhat is the magnitude of the potential difference between points A and H?
a) 100V
b) 200v
V6-Vw: /cr:v * (+rtov)
= 600v
11. What is the
directiqr of the electric field at point E?
E@i
b)
toward B
c) toward H
d) toward C
e) toward F
12. How much work is required to move a +6 pC point charge from B to F to D to A?
a)
+1 .2x10-3 J
+3.6iI0-3.6x10-3 J
zero joules
\N=-A:Pf'€
6uc
=
fttYa-vu)
(r"ov * o)
- I' 2 x ri3f
problems: Provide clear and logical answers to the following questions. Where
euestions and
calculations are required, neatly show all work. Be sure that your answers have the correct units.
1 (20 Points) Four capacitors are connected
values of Cr
:
5.00 pF,
Cz:7 .00 pF, C3 :
below. The capacitors have
5.00, and C+: 3'00 pF'
in
a system as shown
a) Determine the equivalent capacitance of the system.
b) Determine
c) Determine
d) Determine
the total charge that the system can ho1d.
the charge on each capacitor.
the potential difference across each capacitor'
a) J=J-**
c1 Lx
cr
?,?# 4
q=d
ta
ll
=
r'
{,tF 74f
II
,
| 4 L-+L
ut/
L?
v)
uB
,l
I
l
f,rtf-
34r
3S
4F
-g
----.
t{
47
C E= l' 8s /"{tr
*!i},ft
r)
(--
a
v
.o.
AV
CE :
S=
(quf): Wg'ffi a6
f.grr'g5. h*../d stu( g{'*rgt
t
{e'fs
&a
Qr=CrAV= Q, =
4C
G?T : P.,?s dd fl '##
d'}
clB -
cF Av
= d= = Qt
'ca'P{
14
{er $. hu,tt '-,t'/'f r ntt''i}
:
/
tl!,
16? ,A 4C
?*
l'fTrls,
t&i${=3,yv
,
AE=
('J"r r
1"*-r4F
A4$U{--- Fa,6(
'"AVr = {t,: t t4tr
,"' ff)V
g1ru
= l!3:Wi*E,V{
*-j7,5V
n
'
*'t/a.
ffi.'Uffi
',*
+. 34f
t"'/ a =
- -7ld f
Qg :
,A
AJ
-r&,?a l#fl- l''.s-'.$"#-sr
Cs AV
Qt= +,74r
c)
*
Crt
c.F, -ry,?-rytr
cts
2 (20 points) The membrane that surrounds a certain type of living cell has a surface area of
S.dxlg:e m2 and a thickness of 1.0x10-8 m. Assume that the membrane behaves like a para1le1
plate capacitor and has a dielectric constant rc:5.0. The potential on the outer surface is 60. mV
greater ihutr ott the inside surface. (In some sense, it is the discharge of this capacitor in response
to stimuli that creates an electric signal in neurons.)
a) What is the capacitance of this configuration?
b) How much electrical energy is stored in the cell membrane configuration?
c) Determine the charge on each surface.
d) Find the electric field between the two surfaces.
-
6o
r"'{
(-r: {
t\
a^
F
---
1A=
0
::*
yl0-q rr,*
1
"* 8'
lK/D - t"{1
I
,
A€o
c
'
d
2,71 ),il
i
&:
h
-5
Sd
c)
d)
Q -* t
|
Jx,
,?S l(i".) 'Y T
A{
:
I \AVI
-V,
It tl'" s n':
Ar1
a
'
i
L
-," I i
b;
T'.tr--
t^t
-ld t"'/
q
#-
{=
!.
r"
>
v
ga,ly. 6t&r 6*,*
I*i-rL. l=
&rx ,c*3 v
ll
,'.:*
tr
P"
,
5 f2
#S.l "tJ tr (urx';*v)
vJ
:'
4"
t': \
i:.
tisv
:
; '?
t ri
l, 7,3{
(\/
6
u.'
3) (20 points) Consider
a
proton at a certain location in space.
a) Calculate the electric potential produced by this proton at a distanc e 5.29x 10-11 m from
the proton. Call this point A. (This is approximately the distance between the electron and the
proton in the hydrogen atom)
b) What would be the electric potential produced by the proton at avery large distance be?
Call this point B.
c) Determine the work needed to move and electron from point A to point B. This is the
ionization energy of hydrogen.
a)
0
vh=u.t
W
7
-ta
'
1,6
wo
f
a q^to-"
'c
n
t
I
t
I
I
I
I
Vp = t'Iq x/o'l.
o
I
I
6)
B
= 27, AV
b) Vs=o
c)
w=-
r ?Fr: - r (\/-- V*)2n(:t,oxl;tz )Caz^)
wl-Y3.s2rto-t?d
\
\
-ls
= -V,?f)xt7
f