Ex1_solns - Clark Musselman, Ph.D.

*on", &r'r,!LSpring 2015 - Physics 162 - Exam
1
Instructions: All work must be shown on this exam packet. No work on scrap
paper will be accepted. No books or calculators. No notes except for a 3x5
notecard.
(2 points each) For problems 1.-5, circle the bmt answer.
1. X and Y are two uncharged metal spheres on insulating stands, and are
in contact with each other. A positively charged rod R is brought close to
X. Sphere Y is now moved amray from X. What are the final charge states
of X and Y?
(a) Both X and Y are neutral.
(b) X is positive and Y is neutral.
(c) X is neutral and Y is positive.
@* is negative and Y is positive.
(e) Both X and Y are negative.
2. Two identical small charged spheres are a certain distance apart, and
each one initially experiences an electrostatic force of magnitude F due to
the other. With time, charge gradually leaks off of both spheres. When
each of the spheres has lost half its initial charge, the magnitude of the
electrostatic force will be
(a) 1/16 F.
(b) 1/8 F.
6,)ttap.
Y'
(d) 1/2F.
3. A piece of plastic has a net charge of *3.20 pC. How many more pnrtons
than electrons does this piece of plastic have? (e : 1.60 x t0-1e C)
(6\r.oo x 1013
(b) 2.00 x 101e
(c) 4.00 x 1013
(d) 4,00 x 101e
(e) none ofthe
above
Four equal negative point chargee are located at the corners of a square,
their positions in the xy-plane being (1, 1), G1, 1), (-1, -1), (1, -1). The
electric field on the x-anis at (1, 0) points in the sa,rne direction as
i
(u)
(b) ,
vAr-t
(d) i
(e)
-j
A point charge Q is located a short distance from a point charge 3Q, and
no other charges are present. Ifthe electrical force on Q is F, what is the
electrical force on 3Q?
(a) F/3
rb) F/ 3
6"',
(d)
3F
(e) 3F
(10 points) The electric field 2.0 cm from a small object points away from
the object with a strength of 270,000 N/C. What is the objects charge?
KX
rL
x=
Er'
t(
= Q*ouD l)
1,0 x/04
= Qx,,o* ) (,
]lt
rlcl'l
z)'
(,o znt)
Mn'
cz
'
7.
(10 points) What is the force in the c-direction, (F),, on the 5.0 nC charge
in the figure?
l0
nC
O
.1.0
-10 nC
i9-.r---1
,,
-\
G,&4
J
v
5in0 -- 5
W
8rx/01
ynL
=
18 y tou
= tq x/ o-{
-1-1
*,t)
M
(il; (- 'u)e)
Yl0
rt-
hn*
erct',^
(i\
\ +/x =o
5.0 nC
--
Pr,^
cm
,
F*
F*= L*
I6,0,r)Qonc)
tv
o
8.
(S-points each) An electric dipole is formed from two charges,
*q, spaced
1.0 cm apart. The dipole is at the origin, oriented along the'y-axis.
elmtric field strength at the point (x, y) = (0 cm, 10
i.
""r)
(a) What is the charge q?
Cn/
La&
The
abO U7C.
x zkls
f7
*n
E13
@6
o
locw^
ZKS
Ot
Q*L)t.a:
=
z,Eo"/o,
36o Yio-l
y)Q,^)
lX x/0?
_tO .a
(b) What is the dipole moment
f=Qs,
Cr,^- A
B"?
" "h*)
=@ vto-tuc)Ccr ) i
-tz cn
=ZO x/o
i
=ZOxlO C
c