Download Phy2140 Exam 1 SpSu2..

Name:
Class: Phv 2140
Date:
ID: A
May 24,2006
Physics 2140: Exam 1
Multiple Choice (7 points each)
Identify the letter of'the choice that best completes the statement or answers the question.
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1. Very large capacitors have been considered as a means for storing electrical energy. If we const~ucteda very
large parallel-plate capacitor of plate area 8.0 m2using paper ( K = 3.7) of thickness 2.0 mrn as a dielectric,
~ 8.85 x 1VI2CZ/N.m2)
how much electrical energy would it store at a plate voltage of 3000 V? ( E =
(-a. 0.59 J
b. 90 000 J
N ; h
c0&4
c. 9 0 J
d. 45 000 J
e. 9 000 J
- / 1 3 1 ~ l oF
3
C-
4
-
-
-'
2. Which of the following best characterizes electrical conductors?
a. poor heat conductors
b. total electric charge is zero
c. low mass density
d. high tensile strength
C e . electric charges move freely
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3. The resistance of a platinum wire is to be calibrated for low-temperature work. A platinum wire with
resistance 3.000 R at 20°C is immersed in liquid nitrogen at 77 K (-196OC). If the temperature response of
the platinum wire is linear, what is the expected resistance of the platinum wire at -196OC? c+,~.,~..~= 3.92 x
1 v 3PC)-]
a. 1.768 n
LNAT)
b. 0.232 R
So
AT = -(9L0C - 2 3 2
c. 2.757 R
d. 1.847 R
3n (I 3.9240
-2162
K = R, ( I
R=
=
L
A
d'p ; r
-'.(-zlaj
0,Y 60
--
R,= 202
uah.(.
fi
*y
G
~
K
4. A point charge of +8.0 /.LCis located at the origin of a coordinate system and a second point charge of -4.0
pC is at x = 1.0 m. At what point on the x axis is the electrical potential zero?
i s oePahk XCy,
a. +0.25 m
/ $2
b. -0.33 m
n/efF:t&*k/
f,
0
c. +0.75 m
-0.25 m
I -)c
= kc
+-I
<bIw
t
x
A'
Ylj(P!J:
1
I
r
-X = O*&6
kb~?~ -- X =
8
1
ID: A
-
5. If C = 5 1 pF, deterthine the equivalent capacitance for the combination shown.
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6. In x-ray machines, electrons are subjected to electric fields as great as 6.0 x lo5 N/C. Find an electron's
acceleration in this field. (me= 9.1 1 x I@]] kg, e = 1.6 x l@19C)
F
a. 3.6 x lo8 m/s2
.
-
mN
7. Two point charges, separated by 4.5 cm, have charge values of 2 p C and -9.0 pC, respectively. What is the
e mutual force between them? (k, = 8.99 x lo9 N.m2/C2)
c.
d.
e.
16N
3.6 x 1W8N
8.0 x 1@12N
g = 2.-c
c =L/.~C&
rz
',EL = - ?PC
PU
Name:
ID: A
0
--
8. An electric car is
electric motor
"out of juice?"
c.
d.
e.
3000km
2250 km
1500km
'
=
I
J / i
batteries with total energy storage of 5.0 x lo7 J. If the
speed of 30 m/s, how far will the car go before it is
,Car
fi'me
i=
UJEJ
2OOC)W
c c l l o ~
-
ga
x=
=
wt'2 S
r-5,.
l h
~3b.t:
s/c,oFJ2 3 3 0 7iac
.
bJki/e
2 S 0 d 0 dpr.
30 */5 2 a o o3 =
b
A
E d .
v-t
hn / f z r 8 t
7'50 000 m 5 --====
750
9. An electron is released from rest at the negative plate of a parallel-plate capacitor. If the distance across the
plate is 7.0 mm and the potential difference across the plate is 3.0 V, with what velocity does the electron hit
the positive plate? (me = 9.1 x l t 3 ' kg, e = 1.6 x l t I 9 C)
10. A charge, +Q, is placed inside a balloon and the balloon is inflated. As the radius of the balloon r increases the
number of field lines going through the surface of the balloon:
a. decreases as lir.
b. decreases as l/r2.
# o f ,$/A
.
stays the s a m e 2
IL_ b-1 L.OOY\
= FIUX a-d
d. increases proportional to r.
e. increases proportional to r2.
S:
LNW
x ; Qeqc -
AJ-
G,
--
CF/V
-
11. If a 4000-W heater carries a current of 1 .OO A, what is the resistance of the heating element?
a. 11.2R
b. 42.8 R
c. 10.0 n
-
J x ~
e~;lf
Name:
--
ID: A
u
12. A metallic
a.
of I8 x 1 t 6 Q m . What is the resistance of a piece that is 90 m long and
160Q
Short Answer (16 points)
Please show your work in solving this problem. No credit will be awarded for answers without evidence of work
supporting the answer
13. An electron with velocity v = 4.0 x lo6 mls is sent between the plates of a capacitor where the electric field is
E = 900 Vlm. If the distance the electron travels through the field is 4.0 cm, how far is it deviated
in its
path when it emerges from the electric field? (me= 9.1 x I t ' ' kg, e = 1.6 x l t I 9 C)
(u
4+4
cm-Y
VVVVVV
*
~ / ~ = f * i bc e l l
14
,T;-
h-~uc(
19 ~ LikPe-
4c-=
O.OY*r.
fa
,z ~ A
y -At>