1
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printout
should
have
12
questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
be±ore answering.
The due time is Central
time.
Potential Dif
25:02, highSchool, numeric,
>
1 min, normal.
001
The work needed to carry a 1 C charge ±rom
point A to point B is 10 J.
Calculate the potential di²erence between
point A and B.
Correct answer: 10 V.
Explanation:
Let :
q
= 1 C
and
W
= 10 J
.
The work is
W
=
q V
V
=
W
q
=
10 J
1 C
=
10 V
.
keywords:
Point Charge
25:05, trigonometry, numeric,
>
1 min, nor
mal.
002
At distance
r
±rom a point charge
q
, the elec
tric potential is 600 V and the magnitude o±
the electric feld is 200 N
/
C.
Determine the value o±
q
.
Correct answer: 2
.
00277
×
10

7
C.
Explanation:
Let :
k
e
= 8
.
98755
×
10
9
N
·
m
2
/
C
2
,
V
= 600 V
,
and
e
= 200 N
/
C
.
E
=
k
e
q
r
2
and
V
=
k
e
q
r
,
so that
V
E
=
r
.
The potential is
V
=
k
e
q
r
=
k
e
q
V
E
=
k
e
q E
V
q
=
V
2
k
e
E
=
(600 V)
2
(8
.
98755
×
10
9
N
·
m
2
/
C
2
) (200 N
/
C)
=
2
.
00277
×
10

7
C
.
keywords:
Four Charges on a Triangle
25:06, trigonometry, numeric,
>
1 min, nor
mal.
003
Let
²
0
= 8
.
85419
×
10

12
C
2
/
N
/
m
2
.
An equilateral triangle with sides 54 m has
charges +3
μ
C,

3
μ
C, and

9
.
7
μ
C at its
vertices and charge +19
.
4
μ
C at the midpoint
on its side between the vertices with charges
+3
μ
C and

3
μ
C, see the fgure below.
54
m
27 m
27 m
+3
μ
C

3
μ
C

9
.
7
μ
C
P
+19
.
4
μ
C
What is the magnitude o± the
x
component
o± the electric feld at
P
, the point ±orming
a second equilateral triangle with +3
μ
C and

3
μ
/
C.
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 Spring '10
 Avram
 Physics, Work, Correct Answer, Qin

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