Physics 2220
Spring 2014
Paolo Gondolo
EXAM 2
PLEASE FILL IN THE INFORMATION BELOW
Name (printed):
Name (signed):
Student ID Number
Discussion Instructor:
U __ __ __ __ __ __ __
Anthony
KC
Matt
Paul
Peter
Important!
You are not required to answer all questions in this exam. You will receive points
toward your exam points for every question correctly answered. Partial credit is
available, however a minimum amount of work and explanation must be shown to
receive any credit (for example, a mere list of equations with no explanation of their
connection to the problem will not receive credit).
Physics 2220
Spring 2014
Paolo Gondolo
Data: Use these constants (where it states, for example, 1 ft, the 1 is exact for significant figure purposes).
1 ft = 12 in (exact)
1 m = 3.28 ft
1 mile = 5280 ft (exact)

x


x 2  a 2 dx 
1
3

x2  a2

3
1 hour = 3600 sec = 60 min (exact)
1 day = 24 hr (exact)
2
2
gearth = 9.80 m/s = 32.2 ft/s
gmoon = 1.67 m/s2 = 5.48 ft/s2






dx
 x2  a2 
3

x
a2 x2  a2
1 year = 365.25 days
  ax
e
dx


1 kg = 0.0685 slug
1 N = 0.225 pound
1 horsepower = 550 ft‫ڄ‬pounds/s (exact)
24
Mearth = 5.98 × 10 kg
Rearth = 6.38 × 103 km






Msun = 1.99 × 1030 kg





Rsun = 6.96 × 108 m
22
Mmoon = 7.35 × 10 kg
Rmoon = 1.74 × 103 km
G = 6.67 × 10-11 N‫ڄ‬m2/kg2
9
2
2
k = 8.99 × 10 N‫ڄ‬m /C





εo = 8.85 × 10-12 C2/(N·m2)
eelectron charge = -1.60 × 10-19 C
melectron = 9.11 × 10-31 kg





μo = 4π × 10-7 T‫ڄ‬m/A (exact)
N(Avogadro's No.) = 6.02 × 1023 atoms/gm‫ڄ‬mole
26
= 6.02 × 10 atoms/kg‫ڄ‬mole
cos(a ± b) = cos a cos b ‫ ט‬a sin b
xdx
 x2  a 
2 3/2
xdx
a2  x2

1
x2  a2
  a2  x2
dx
 n  x  x 2  a 2 


x2  a2
1  a  x 2  a 2
  n
a 
x
x x2  a2

dx
x a





x
x
 sin 1   , or  cos 1  
a
a
a2  x2
xdx
2
2
 x2  a2
dx
sin(a ± b) = sin a cos b ± sin b
mproton = 1.67 × 10−27 kg
h = 6.64 × 10-34 J
π = 3.14
8
c = 3.00 × 10 m/s









1 Tesla = 10,000 gauss (exact)
ρ(H2O) = 1000 kg/m3
1
  eax
a









dx
1
 n  a  bx 
a  bx b
dx
 a  bx 2

1
b  a  bx 
Physics
Physics2220
2220
Fall 2009Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
Answer the following questions for the AC circuit on the right.
(a)
(b)
(c)
[10 pts.] What is the rms current through the 200 mH inductor?
[10 pts.] What is the rms voltage across the 200 mH inductor?
[10 pts.] To bring the circuit to resonance, should the frequency of
the AC source be increased or decreased from the value indicated?
Justify your answer.
Paolo Gondolo
1
Physics
Physics2220
2220 Fall 2009
Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
The 10-turn loop of wire shown in the figure lies in a horizontal plane, parallel
to a uniform horizontal magnetic field, and carries a 2.00 A current. The loop
is free to rotate about a nonmagnetic axle through the center. A 50 g mass
hangs from one edge of the loop.
(a)
(b)
(c)
[10 pts.] What is the magnitude of the magnetic dipole moment of
the loop?
[10 pts.] What magnetic field magnitude will prevent the loop from
rotating about the axle?
[10 pts.] For this to happen, should the current in the loop flow
clockwise or counterclockwise (as viewed from above)? Explain
your reasoning.
Paolo Gondolo
2
Physics
Physics2220
220
Fall 2009Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
[10 pts.] What are the magnitude and direction of the magnetic field at
the center of the loop in the figure, assuming the straight wires are very
long?
Paolo Gondolo
3
Physics
Physics2220
220
Fall 2009Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
A flexible circular loop 6.50 cm in diameter lies in a magnetic field with magnitude
0.950 T, directed into the plane of the page as shown in the figure. The loop is
pulled at the points indicated by the arrows, forming a loop of zero area in 0.250 s.
(a)
(b)
[10 pts.] Find the average induced emf in the circuit.
[10 pts.] What is the direction of the current in the resistor R, from a to b
or from b to a? Explain your reasoning.
Paolo Gondolo
4
Physics
Physics2220
220
Fall 2009Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
A metal rod of length L = 50.0 cm is suspended from two springs of spring
constant k = 100 N/m as in the figure. It is connected to a 12.0 V battery to
form a circuit of total resistance R = 0.1 Ω. A uniform magnetic field
B = 100 mT is directed horizontally perpendicularly to the rod (out of the
page). After the switch is closed, the rod moves to a new equilibrium
position.
(a)
(b)
[10 pts.] In which direction does the rod move? Explain your
reasoning.
[10 pts.] By how much does the rod move?
Paolo Gondolo
5
Physics
Physics2220
220
Fall 2009Spring 2014
Name: __________________________________
Unid: ___________________________________
Discussion TA: ___________________________
Exam 2
Show all work!! Report all numbers to three (3) significant figures.
A 400-turn solenoid of length 25.0 cm and radius 2.00 cm carries a current of 3.00 A.
(a)
(b)
(c)
[10 pts.] Find the magnetic field inside the solenoid.
[10 pts.] Find the self-inductance of the solenoid.
[10 pts.] Find the magnetic energy stored in the solenoid.
Paolo Gondolo
6
1'11\~ll~
"prin~ 2014
2220
Paolo (,ondolo
Name: -------------------------
Unid: ----------.--------------Discussion TA: _.___:P..:;..e-..;;..W..;;.._____________
1
Exam2
Sbow all work!! Reoort all numbers to three (3) significant figures.
Answer the following questions for the AC circuit on the right.
(a)
(b)
(c)
200mH
[10 pts.] What is the nns current through the 200 mH inductor?
[1 0 pts.] What is the nns voltage across the 200 mH inductor?
[10 pts.] To bring the circuit to resonance, should the frequency of
the AC source be increased or decreased from the value indicated?
£rrns = 10 V
f =200Hz 4 ·0 ¢'
2.0 ¢'
Justify your answer.
e~HS
(a.)
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=
lt.l
C = C,+ ~:.
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f
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::::
I
--
C2HS
'2.R f L -
= ~4.2 t'HA
2u:f(!.
I -\
------===---
~
Name: --~--~--~~?______________
Unid: _ _ _
4...:__/V_S_~_t__;y;__l_ _ __
Discussion TA: ....:·--,------------
2
Exam2
Show all work!! Belgrt all numbers to three (3) significant figures.
The 10-tum loop of wire shown in the figure lies in a horizontal plane, parallel
to a unifonn horizontal magnetic field, and carries a 2.00 A current. The loop
is free to rotate about a nonmagnetic axle through the center. A 50 g mass
hangs from one edge of the loop.
(a)
(b)
(c)
10 turns
{10 pts.] What is the magnitude of the magnetic dipole moment of
the loop?
[10 pts.] What magnetic field magnitude will prevent the loop from
rotating about the axle?
[10 pts.] For this to happen, should the current in the loop flow
clockwise or counterclockwise (as viewed from above)? Explain
your reasoning.
ort-S'. ... -'>
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Name:
-----------------------
Unid: - - - - - - - . . . , - - - - - - - - Discussion TA: ____:...f~e~f.lL.-':::e;..:..r_______
Show all work!! ReQOrt
3
Exam2
an numbers to three (3) significant figures.
5.0A
[10 pts.} What are the magnitude and direction ofthe magnetic field at
the center of the loop in the figure, assuming the straight wires are very
long?
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Paolo ( .ondolo
"'prill!!. 20 1-t
Name: -----------------------Unid: ----------,--------------Discussion TA: _;,_~fV1~,.._~J.-:!....f::L-----------
4
Exam2
Show all work!! Reoort all numbers to three (3) significant figures.
\
A flexible circular loop 6.50 em in diameter lies in a magnetic field with magnitude
0.950 T, directed into the plane of the page as shown in the figure. The loop is
pulled at the points mdicated by the arrOWS, forming a loop Of zero area in 0.250 S.
x
(a)
(b)
X
X
[10 pts.] Find the average induced emf in the circuit.
{ 10 pts.] What is the direction of the current in the resistor R, from a to b
or from b to a? Explain your reasoning.
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Name: --~~~--------------­
Unid: - - - - - - - - - - - - Discussion TA: _,_________________
5
Exam2
Show all work!! Reoort all numbers to three (3) significant figures.
A metal rod of length L = 50.0 em is suspended from two springs of spring
constant k = 100 N/m as in the figure. It is connected to a 12.0 V battery to
form a circuit of total resistance R = 0.1 n. A uniform magnetic field
B = 100 mT is directed horizontally perpendicularly to the rod (out of the
page). After the switch is closed, the rod moves to a new equilibrium
position.
k
(a)
[10 pts.] In which direction does the rod move? Explain your
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(b)
reasoning.
{10 pts.] By how much does the rod move?
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l'h''il' 2211
Paolo (,ondolo
"Prill!!, 2014
Name:----------
Unid: - - - - - : : : : - - - - - - - Discussion TA: _._?_a~<....._J. . .). _ _ _ __
6
Exam2
Show all work!! Reoort all numbers to three (3) significant figures.
A 400-tum solenoid of length 25.0 em and radius 2.00 em carries a current of3.00 A.
(a)
(b)
(c)
2; , C) c~
r-=2 ,CJo c""'
.R, -=-
{10 pts.] Find the magnetic field inside the solenoid.
{10 pts.] Find the self-inductance of the solenoid.
[1 0 pts.] Find the magnetic energy stored in the solenoid.
d
-=- ( t£ 17 rf
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t ff(!)c)) { j)
-=- DrO~()J T
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