General Physics II (PHYS 104)
Exam 3: April26,2012
Name:
Multiple Choice (4 points each): Answer the following multiple choice
questions.
Clearly circle the response (or responses) that provides the best answer to the question'
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.
l) A 4.5-V battery is cormected to two resistors connected in series
as
shown in the drawing. Determine the total power dissipated in the
resistors.
A)
0.033
W B) o.oeo w
F=TAV=4It=
Reb
tffil
?*T
(t.r
4rv-f-l;?"-l
-/\A/\,-
-L---^nF--l
D) o.6ow E) 4.7w
v.,1
).lrf ? w
=
l34L
t
2) When resistors are connected in parallel, we can be certain that
a. the same current flows in each one.
@ ttre potential difference across each is the same'
c. the power dissipated in each is the same.
d. their equivalent resistance is greater than the resistance of any one of the individual
resistances.
3)
Three resistors, 6.0-f), 9.0-f), 15-f), ale connected in parallel in a circuit. What is the
equivalent resistance of this combination of resistors?
0.34CI
B)
c)
A)
3.8"mE)
| + -L =
_t_ +
'
6JL IJL' /rn
1oo
3oo
I
Ra
lt +Jg
' ?otL =4
'
l orz
Jost
?on
R,,=fu
3t
4) The figure shows a simple RC circuit consisting of a 10-prF capacitor in series with a resistor.
Initially, the switch is open as suggested in the figure. The capacitor has been charged. The
potential difference between its plates is 100 V. At /: 0 s, the switch is
,________44A/\_,
closed. The capacitor discharges exponentially so that 2.0 s after the
switch is closed, the potential difference between the capacitor plates is 37
V. In other words, in 2,0 s the potential difference between the capacitor
plates is reduced to 31 %o of its original value. Determine the numerical
value of the resistance R.
l,o* n
Lll--*,r
A)
1.0
x
(r
105
{?c
(:k
D)
1.0 x 106 f)
el
=<-tZ
/0
Page
1
xtf
a
?x/0
E) 2.5 x 106 f)
I
5)
Kjrchhoffs junction rule is an example of
@ conservation of energy.
b) conservation of charge.
c) conservation of momentum.
d) none ofthe above.
6) Ar overhead electric power line carries a maximum current of 125 A. What is the magnitude
of the maximum magnetic field at
a
point 4.50 m directlybelow the power line?
f"Ja t.tu x 1o-6 r
b)
1.75 x 10-5 T
c)
3.49 x 10-5 T
$: 4.
lrt
d) 4.69 x 10-4 T
e) 7.95 x 10-3 T
T
I fir*
-
R
t) =\+TrUi7
;1rp- Q;^
electron is moving with a speed of 3.5 x 105 m/s when it encounters a magnetic field of '
0.60 T. The direction of the magnetic fie1d makes an angle of 60.0o with respect to the
velocity of the electron. What is the magnitude of the magnetic force on the electron? B
A) 4.9 x 10-13 N
V = 7.rrv,f ,rR
B=
B) 3.2 x 10-13 N
C) 1.7 x 10-13 N
7) An
;jCfrt
*'7
u
Ss xtd;l
'w'
8) A long straight vertical segment of wire traverses a
magnetic field of magnitude 2.0 T in the direction
shown in the diagram. The length of the wire that lies in
the magnetic field is 0.060 m. When the switch is
closed, a current of 4.0 A flows through the wire from
point P to point Q. What is the magnitude of the
magnetic force acting on the wire?
A) 0.12 N
D)67N
(r,indo
n:;,;|7inf,
f = e7 No-/r t
F=flB = [n(,06r\) 2,aT:,ffr
E) zero newtons
Page2
9) A uniform magnetic field cannot exert a magnetic force on a particle in which of the foliowing
circumstances? (Select all that apply.)
particle is at rest.
particle
is charged.
B) The
C) The particle.moves perpendicular to the field.
D) The magnitude of the magnetic field changes with time.
fne particle moves parallel to the field.
@ffr.
@
10) Two long parallel wires caffy culrents of 5.0 A and 8.0 A in the same direction. The wires
are sepggte(hy.rllrdind the ma.qnetic fo4ce between I meter segments of the two wires.
--
fI lli htruhrt.
';=b+!=3.N;7'#
ffil{
b)7.2x10-5Nrepulsive
llll
ll 'r
P'ft
-Z
fl: ?6ZX/0'N= l,b7x/;SN
1t) A proton moving horizontally enters a region where a uniform magnetic field is directed
perpendicular to the proton's velocity, as shown in the figure below. After the proton enters the
field, it does which of the following?
S
:,:/,
S
:\ri
,t'
{#--"-*---F.'-ut .
f"
'g
,
trr
A) deflects into the paper
B) deflects out of the paper
C) dr.fl€$g dqrypryard
Page 3
Questions and Problems: Provide clear and logical answers to al1of the following questions.
Where calculations are required, neatly show all work. Be sure that your answers have the
correct units. Questions are worth 15 points each.
1) Consider the circuit shown at the right.
a) Determine the equivalent resistance of this circuit'
b) What is the current that flows from the battery?
c) Determine the potential drop from point A to point B.
d) Determine the potential drop from point A to point D'
q
0)
(n
7fn\
yRn=
|
RB
\-^^-tl
6fr
o(
-ry
3Jr
c)
.J =7
rQz
(F = 7{L
.:
6ti
N-=
R-
b)
I
AVnc = TgP
At
IB= Tc
S
=
R,?
A { no= 4&u
d)
=
6/
/{L
=ln
14 stt= 3t/
4vetd, .t,
*
4
A{n, =qD
d{L
& Aunp= rD &p= lA an= *
RD
+
Page 4
tfr
2) Consider the circuit shown in the figure to the right. (Note
R1:22,C), Rz: 1 5 f), V1 :9.0V, V3:6. 0V)
a) Apply Kirchhoff s Loop Rule to the bottom loop to
determine Iz.
b) What is the current through Rl?
1b
a) lvz+ TlPz = o
-'*
r)
G^-
R2
tloyqQ)
(w*t
-.YA
€v
, /in
ov* er loop
-r,Qt
A(, +
AVs
.rf
AVt Av,
l-
20
_
q r+dv
f
E'TL
k,,
Page 5
c
H=,dgn
A mass spectrometer is a device used to identify the composition of materials and elucidate
the structural and physical properties of ions. This instrument will separate charged atoms or
molecules according to their mass-to-charge ratio. First, the material to be analyzed is ionized
and vaporized. The ionization process may, for example, remove an electron from a particle,
3)
leaving it with a net positive charge. The ions are then accelerated through a potential difference
and enter a region of constant magnetic field. These ions, traveling with a velocity, v, are
deflected by the magnetic field and travel in semicircular paths. The detector is adjusted so that
it will only detect those ions that follow a path of a certain radius. Thus, different materials can
be distinguished from one another. Consider this mass spectrometer experiment and answer the
questions that follow:
beam consisting of 5 types of ions labeled A, B, C, D, and E enters a region that
contains a uniform magnetic field as shown in the figure below. The field is perpendicular to the
plane of the paper, but its precise direction is not given. A11 ions in the beam travel with the
same speed. The table below gives the masses and charges of the ions. Note: 1 mass uniF1.67 x
A
1o-27kg
Ion
X
X
{tr:girl*r
r:$(r*lr:iff
X,'-R ("-*{ f
nlilgn*1id l:thl
]A';.i
fr
ffi
irirt
a.) Which ion falls at position
lirlrti
Mass
Charge
A
2 units
*e
B
C
D
E
4 units
*e
6 units
+e
2 units
-e
4 units
-e
2?
b.) What is the direction of the magnetic field?
T"ta
?#,
c.) Determine the magnitude of the magnetic fie1d if ion A travels in a semicircular path of
'::
a sPeed
r.= ila'f
ffi
"";::fi
v=T ,' W
$=
*&
,)t{Y ,)lT
Page 6
F
//o'%
4) Two long, straight wires separated by 0.10 m carry currents of 1 8
and 6 A in the same direction as shown'
a) Determine the magnitude and direction of the magnetic
produced at P bYthe 18 A current.
A
6A
field
F
b) Determine the magnitude and direction of the magnetic field
produced at P bY the 6 A current'
c) Determine the overall magnetic field at point P.
d) Determine the location where the magnetic field is zero'
(lt
A) Inttt Wer' (3J
B*= 4, E = fYi'ry'Y^ -- ),+ xl;t.7ft '/f,an
r
at
rt)
T^t-u pop(r
b)
3)
=9
t=
27r r
#
?16'T #^=
) g= ts6t136 i"
v,tr
l</o-rr ftf, fc^,o/r.
BB
c
(
TtxrirT'
\r-1--l
fa'qtu'c r
Ju
cl\
B
et-
,+^
7 (,,...8 P
c
ol
ir t &t',ra'
itla Pf t' , BF
Aefu:Ib
a'il'' G
of VPcr'
r^
fit
-l
IatIs
-q) =rBq
,l(*)
nB
14&(.t
,y^
out'
Page 7
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