unl department of physics and astronomy · preliminary examination – day 2 august, 2011 this test...
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UNL Department of Physics and Astronomy
Preliminary Examination – Day 1
August, 2011
This test covers the topics of Mechanics (Topic 1) and Thermodynamics and Statistical
Mechanics (Topic 2). Each topic has 4 “A” questions and 4 “B” questions. Work 2 problems
from each group. Thus, you will work on a total of 8 questions today, 4 from each topic.
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Mechanics Group A. Answer only 2 Group A questions.
A1. The trajectory of a body of mass m, measured in a frame A, is given by
v ,
where v0, g, ω, x0, and y0 are constants. The force applied to the body is known to be
.
Is the frame A inertial? Explain.
A2. A mass m is attached to a spring and is oscillating as x = Acos(ωt + φ). A very short
impulse is to be applied to the mass to stop the motion. What is the magnitude of the impulse?
When must it be applied?
A3. Consider two cylindrical bodies (A and B) of equal mass and dimensions with moments of
inertia about the cylindrical axis of IA and IB, respectively. For both bodies, the center of mass
coincides with the geometric center. Each is released from rest and allowed to roll down an
inclined ramp. Assuming the center of mass of each body is initially at the same location, which
body will have the greater center of mass velocity at the bottom of the ramp. Why?
A4. A particle of mass m moves in a potential V(x) = βx4 – αx2, where α and β are constants and
are both greater than zero. Find the equilibria and determine their stability. Find the frequency
of small oscillations of a mass about the stable equilibria. What are the dimensions of α and β ?
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Mechani
B1. A sa
the satell
This puts
radius r2
B2. For t
where k
(a) Find t
(b) Are th
momenta
(c) Find t
B3. A b
inclined
wedge is
Find the
B4. A pa
can swin
masses a
angle θ.
ics Group B
atellite is in
lite’s engine
s the satellit
at perigee (c
the Lagrangi
and m are co
the equation
here any ign
a?
the energy o
block of mas
at an angle θ
s μ. As the su
coefficient o
air of masses
ng in the plan
are also conn
. Answer on
a circular or
e is used to r
te into an el
closest dista
ian
onstants:
ns of motion
norable (i.e. c
of the system
ss m is relea
θ to the hori
urface of the
of friction as
s is attached
ne as shown
nected to eac
nly 2 Group
rbit of radiu
reduce the v
lliptical orbi
ance). Find th
1
. (Don’t try t
cyclic) coord
m. Is it conser
ased from th
izontal. Initia
e block heats
a function o
to a pivot o
n. The shaft i
ch other by a
p B question
us r1 about th
velocity by a
it having rad
he ratio r1/r2
to solve the e
dinates? If so
rved? Why?
he top of a
ally, the coe
s up, μ decr
of the distan
n a vertical s
s rotating w
a spring as sh
ns.
the center of
a factor s wi
dius r1 at ap
as a functio
equations.)
o, what are t
fixed wedg
fficient of fr
reases linearl
nce traveled b
shaft by mas
with a constan
hown. Find
f the Earth. A
ithout chang
pogee (farthe
on of s.
the correspo
ge. The face
riction betwe
ly with the e
by the block
ssless rods o
nt angular fr
the equilibri
A short thru
ging its direc
est distance
onding conse
of the wed
een block an
energy abso
k.
of length ℓ an
requency ω.
ium value o
ust of
ction.
) and
erved
dge is
nd the
orbed.
nd
The
f the
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Thermodynamics and Statistics Group A. Answer only 2 Group A questions.
A1. A die is thrown N times, and the sum of all N shown numbers is recorded. Find the
expectation value and the standard deviation for this sum.
A2. The figure shows the phase diagram for a one‐
component substance. Put labels on the graph to indicate the
areas of the solid (S), liquid (L), and gas (G) phase. If the solid
phase is in equilibrium with the liquid phase at pressure P1,
will the solid float or sink? Is there a pressure at which the
solid will neither float nor sink? Explain your reasoning.
A3. Consider a gas characterized by an unknown equation of state P=P(V,T). Express
in terms of and .
A4. Write down briefly but precisely
A)The Kelvin statement of the second law.
B) The Clausius statement of the second law.
C) The entropy statement of the second law.
T
P
P1
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Thermodynamics and Statistics Group B. Answer only 2 Group B questions.
B1. Two copper blocks (implying constant heat capacity) at temperature Th and Tc, where Tc <
Th, are allowed to equilibrate by means of a reversible heat engine operating between the two
blocks.
a) What is the final temperature of both blocks (when the heat engine stops producing
work) in terms of Th and Tc?
b) What is the total change in entropy of the two blocks?
B2. A reversible heat engine extracts heat Qh from a reservoir at temperature Th and heat Qm =
aQh, with 0 < a < 1, from a reservoir at temperature Tm < Th while rejecting heat Qc to a reservoir
at temperature Tc < Tm.
Derive an expression for the efficiency of this three‐reservoir heat engine in terms of a and the
three reservoir temperatures Th, Tm, and Tc. The efficiency is given by the produced work
divided by the heat extracted from the two hotter reservoirs. Check your result by showing that
the efficiency reduces to the Carnot efficiency expression in the limits a → 0 and Tm →Tc.
B3. 500 grams of ice cubes at 0C are placed in 1 liter of water at 20C. The system then comes
to equilibrium with no heat exchange with the surroundings.
(a) Does the ice melt completely? If yes, find the temperature of the water in equilibrium. If not,
find how much ice remains in equilibrium.
(b) Calculate the total change of entropy for the whole system.
B4. A certain substance in a vessel undergoes the following process:
(a) It expands isothermally while receiving 1000 J of heat from the thermostat at 1000 K.
(b) It is insulated and then expanded somewhat.
(c) It is compressed isothermally while releasing 250 J to the second thermostat at 500 K.
(d) It is insulated and then expanded somewhat.
(e) It is compressed isothermally while releasing some heat to the third thermostat at 300 K.
(f) It is insulated and then compressed in such a way that it ends up in the initial state.
Given these restrictions, what is the maximum amount of work that can be done by the system
in such a process?
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General e
For a Car
becomes
Clausius
/
efficiency η
rnot cycle op
h cC
h
T T
T
’ theorem: N
i
Δ ; specif
EQUA
of a heat eng
perating as a
cT
.
1
0N
i
i
Q
T
wh
fic heat of wa
ATIONS TH
gine produc
a heat engine
hich become
ater: 4186 J/(
HAT MAY B
cing work W
e between re
e 1
0N
i
i i
Q
T
f
(kg*K); Late
BE HELPFU
W while taki
eservoirs at
for a reversi
ent heat of ic
UL
ing in heat
hT and at cT
ible cyclic pr
ce melting: 3
hQ is W
Q
cT the efficien
rocess of N s
334 J/g
h
W
Q.
ncy
steps.
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UNL Department of Physics and Astronomy
Preliminary Examination – Day 2
August, 2011
This test covers the topics of Electricity and Magnetism (Topic 1) and Quantum Mechanics
(Topic 2). Each topic has 4 “A” questions and 4 “B” questions. Work 2 problems from each
group. Thus, you will work on a total of 8 questions today, 4 from each topic.
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Electrici
A1. A p
= d. Ho
infinite,
Larger, s
A2. Con
dielectri
modifies
same? W A3. A ch
and B fie
exactly f
the parti
direction A4. Wh
outer ra
infinites
ity and Ma
positive cha
ow does the
grounded
smaller, or
nsider a regi
ic is then br
s the E field
Why?
harged part
eld. The E
follows the
icle’s charg
n respective
hat is the ma
dius b, and
simally thin
gnetism G
rge q is pla
e net force a
plane cond
just the sam
ion of space
rought into
d. Does the
ticle with ze
field is give
E field. W
ge? (In this
ely.)
agnetic dip
d surface cu
n ring of rad
roup A. An
ced on the
acting on th
ductor is pla
me? Find th
e containin
this region
electrostati
ero initial v
en by E E
What is the d
problem
ˆ i ,
ole momen
urrent densi
dius r carry
nswer only
x‐axis at x =
he positive c
aced in the
he ratio of t
ng an E field
n of space an
ic energy U
velocity ent
E0ˆ i and the
direction of
, ˆ j , ˆ k are uni
nt of a flat c
ity K=K0? ying a curre
y 2 Group A
= 2d and a s
charge com
yz‐plane?
the two for
d. A Linear
nd the pres
UE increase,
ters a region
e particle m
the B field
it vectors al
circular disc
Hint: the d
ent I is r2I.
A question
second cha
mpare to the
Is it in the s
ces.
r Isotropic H
sence of the
decrease o
n containin
moves in a tr
and what i
long the x,y
c with inner
dipole mom
ns.
rge Q = ‐2q
e case wher
same direct
Homogene
e dielectric
or stay the
ng both an E
rajectory th
is the sign o
y, and z
r radius a,
ment of a
at x
re an
tion?
ous
E
hat
of
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Electricity and Magnetism Group B. Answer only 2 Group B questions.
B1. Consider an infinitely long solid cylinder of radius R along the z axis. A current
flows up the wire with a volume current density given by J J0
ˆ z .
(a) Draw a figure indicating coordinate axes, the cylinder and the direction of current
flow. Explain clearly the limitations that the symmetry of this structure imposes on the
B field as well as the limitations resulting from the Biot‐Savart Law.
(b) Using Ampere’s law calculate the B field vector both inside and outside the cylinder.
Draw and describe the Amperian loop to be used in each case.
B2. Consider two dipoles m1 and m2 a distance d apart oriented so that both are
perpendicular to d as shown. m1 is fixed and m2 is free to move in any fashion. (a) Re‐draw the diagram above and indicate an appropriate choice of coordinate
system.
(b) What is the torque exerted by dipole m1 on dipole m2? Describe the resultant motion
of m2 under the action of this torque.
(c) What is the force exerted by dipole m1 on dipole m2? Describe the resultant motion
of m2 under the action of this force.
d m1 m2
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Electrici
B3. A cy
its axis.
magneti
lies in th
(a) Find
the direc
cross sec
(b) Find
the direc
(c) The
boundar
just with
very sm
B4. The
where th
where A
(a) Draw
direction
r=R: at th
(b) Calcu
(c) From
say abou
density
ity and Ma
ylinder of le
The cylinde
ization. The
he x‐y plane
the magnit
ction on the
ctional view
d the magnit
ction on the
B field ever
ry condition
hin the toru
all. Note:
e electric fie
hese refer to
A is a positiv
w a figure o
and magnit
he North p
ulate the ch
m your resu
ut the volum
isotropic?
gnetism G
ength L and
er is then b
e center of t
e. A cut aw
tude and di
e diagram (
ws.
tude and d
e diagram,
rywhere in
ns, calculat
us and on th
There are t
ld in a regi
o the comp
ve constant
of a sphere
tude of the E
ole, at the S
harge densi
ults in (ii) a
me charge d
Justify you
roup B (con
d radius a h
ent into a to
the torus is
way view is
irection of t
(which you
irection of t
on both the
side the “h
te the magn
he y axis i.e
wo tangent
on r > R is g
ponents of th
t.
of radius r
E field at th
South pole,
ity in the re
and from th
density? W
ur answers.
ntinued). A
has a unifor
orus of inn
at the origi
shown belo
the bound v
should red
the bound
e right and
ole” of the
nitude and d
e. at a coord
tial directio
given by
E
he E field in
= R, includ
hree points
and at the
egion r > R.
he E field gi
Where do th
Answer on
rm magneti
ner radius R
in and the c
ow.
volume cur
draw), on b
surface cur
left cross se
torus is zer
direction of
dinate point
ons‐be caref
Er 2Acos
r3
n a spherica
ding approp
at the surfa
Equator.
Show all w
ven in the p
he charges e
nly 2 Group
ization M0 d
R, without c
central plan
rrent densit
both the righ
rrent densit
ectional vie
ro. Using th
f the B field
t (0, R+, 0)ful which o
,
s
r
AE
al coordina
priate axes,
ace of the sp
work.
problem, w
exist? Is the
p B questio
directed alo
changing its
ne of the to
ty, Jb. Indic
ht and left
ty, Kb. Indic
ews.
he appropr
d at a point
) where isone you cho
3
in
r
and
E
ate system a
and the
phere, i.e. w
what can yo
e charge
ns.
ong
s
rus
cate
cate
riate
P
s
oose.
0,
and
with
u
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Quantum Mechanics Group A. Answer only 2 Group A questions.
A1. What is the kinetic energy of an electron that has the same momentum as an 80‐keV
photon?
A2. A particle with mass m is described by the normalized wavefunction
12
cos( / ) for ( )
0 elsewhere
C x a a x ax
,
Where a and C are positive real‐valued constants. If we measure the particle’s
momentum, what is the probability that we find it moving to the left? Explain your
answer.
A3. This problem refers to motion in one dimension along the x ‐axis. Is
, Hermitian? Explain.
A4. A three‐dimensional Hilbert space 3H is spanned by the complete set of
orthonormal kets: 1 2 3| , | , and |u u u . At some point in time, the quantum system is in
the state
131 1
1 32 2| e 3 | |i u u .
(a) Show that | is normalized.
At the same point in time, we do a measurement of an observable S with the associated
operator S . We find the non‐degenerate value S s , which corresponds to the eigenket
5 12
2 313 13| | |s i u u .
(b) What was the probability to find this value s ?
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Quantum Mechanics Group B. Answer only 2 Group B questions.
B1. A free particle of mass m , moving in a one‐dimensional space, has the following
normalized wavefunction in momentum space (momentum probability amplitude):
for ( is a real-valued constant)| ( ) 2
0 for all other
hK p K
p p ap
The eigenkets | p of the momentum operator p satisfy completeness: | |dp p p
1.
(a) Find the constant K, including units.
(b) Find the wavefunction ( )x in position space.
B2. A point particle with mass m moves in one dimension (coordinate x ) in the
potential
2 2102
( )V x m x ,
where 0 is a constant. The normalized stationary states are given by
0 1 2( ), ( ), ( ),...x x x for increasing eigenenergies 0 1 2, , , ...E E E , respectively.
At time 0t the system is described by the normalized wave function
10 22
( , 0) 3 ( ) ( )x t i x K x ,
where K is a positive real‐valued constant.
(a) Give the Hamiltonian for this system.
(b) Determine the value of K .
(c) If, at 0t , we measure the energy, what is the probability we find the value 0E ?
(d) Calculate the expectation value of the energy at 0t .
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Quantum Mechanics Group B (continued). Answer only 2 Group B questions.
B3. A beam of electrons (see above) with kinetic energy 10 eVE impinges on a step
with height 0V E . The incoming probability current is 5 1
in 4.0 10 sJ (left to right).
We describe the wavefunction of the incoming electrons as in ( ) ikxx Ae .
(a) Determine the quantities A and k , making sure to include units in your answers.
(b) Demonstrate that the wavefunction IIxBe is the solution of the time‐inde‐
pendent Schrödinger equation in region II. Give an expression for .
(c) What is the probability current IIJ in region II?
(d) What is the reflection coefficient R of this potential step?
At the position Å1.4x d (in region II) the absolute value of the amplitude of the
evanescent wave has dropped to 1% of what it is at the location of the step ( 0x ).
(e) What is the height 0V of the step? Give your answer in eV.
region I
region II
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Quantum Mechanics Group B (continued). Answer only 2 Group B questions.
B4. The wavefunction of a particle moving in one dimension ( x ) is given, at some time,
by
0 / 2 2 for ( )
0 elsewhere
ip xK e b x b x bx
in which 0p and the normalization constant K are positive real numbers.
(a) Calculate the normalization constant K . What are the units of K (SI) ?
(b) For the given wavefunction, you measure the particle’s position. Calculate the
probability that you find it between 12x b and 0x .
(c) Give a symmetry argument to explain why 0x (no calculation).
(d) Calculate ⟨ ⟩.
(e) Calculate x .
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Physical Constants
speed of light .................. 82.998 10 m/sc electrostatic constant ... 1 90(4 ) 8.988 10 m/Fk
Planck’s constant ........... 346.626 10 J sh electron mass ............... 31el 9.109 10 kgm
Planck’s constant / 2π ... 341.055 10 J s proton mass ................. 27p 1.673 10 kgm
elementary charge ......... 191.602 10 Ce 1 bohr ............................. 0 0.5292 Åa
electric permittivity ...... 120 8.854 10 F/m 1 hartree ........................ h 27.21 eVE
magnetic permeability ... 60 1.257 10 H/m
EQUATIONS THAT MAY BE HELPFUL
Electrostatics:
E d
A
qenc
0A
E
0
X
E 0
E d
l V (r2)V (r1
r1
r2
) '
'
0
)(
4
1)(
rr
rqrV
Work done W q
E .d
l
a
b
q[V (b ) V (
a )]
Multipole expansion:
V (r )
1
40
1
r(r ' )d '
1
r2r ' Cos '(
r ' )d '
1
r3(r ' )2(
3
2Cos '
1
2)(
r ' )d ' ...
where the first term is the monopole term, the second is the dipole term, the third is the quadrupole term..; r and r’ are the field point and source point as usual and ’ is the angle between them.
D 0
E
P
D f b
P b
P ˆ n
The above are true for ALL dielectrics. Confining ourselves to LIH dielectrics, we also have:
D
E
P e0
E 0(1 e ) e=/0 e e 1
C(dielectric)=e C (vacuum) Boundary Conditions:
E2t E1t 0 E2n E1n 0
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Magnetostatics: Lorentz Force
F q(
v
B ) q
E Current densities
I
J d
A
I
K d
l
Biot Savart Law
B (r )
0
4I
dl ' ˆ 2 where R is the is the vector from the source point r’ to the
field point r.
This can also be written (for surface currents) as
B (r )
0
4
K ˆ 2 d A
For a straight wire segment B 0I
4s[Sin(2) Sin(1)] where s is perpendicular distance from
the wire. For a circular loop of radius R, the B field at a point on the axis is given by
B 0I
2
R2
(R2 z2)3 / 2
For an infinitely long solenoid, the B field inside is given by B=0NI where N is the number of turns per unit length.
B 0
B 0
J Ampere’s law
B d
l 0Ienclosed
Magnetic vector potential A
B
A
2
A 0
J
A
0
4
J
r r 'd '
Also for line and surface currents
A
0
4I
r r'dl '
A
0
4
K
r r'da'
From Stokes theorem
A d
l
B .d
a
For a magnetic dipole m ,
A dipole
0
4
m ˆ r
r2
Magnetic dipoles Magnetic dipole moment of a current distribution is given by m=Ida Torque on a magnetic dipole in a magnetic field =mXB Force on a magnetic dipole
F (
m
B )
B field of a magnetic dipole
B (r )
0
41
r3[3(
m ˆ r )ˆ r ˆ m ]
Dipole-dipole interaction energy is given by
UDD
0
4R3(m 1
m 2) 3(
m 1 ˆ R )(
m 2 ˆ R ) where R=r1-r2
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Material with magnetization M produces a magnetic field equivalent to that of (bound)volume and surface current densities
J b
X
M and
K b
M ˆ n .
H d
l I freeenclosed
H
B
0
M
For linear magnetic material M=mH and B=0(1+m)H or B=H Boundary Conditions: B2n-B1n=0 B2//-B1//=0K Maxwell’s Equations in vacuum:
1.
E
0
Gauss’ Law
2.
B 0
3.
E
B
t Faradays law
4.
B 0
J 00
E
t Ampere’s Law with Maxwell’s correction
Maxwell’s Equations in LIH media :
1.
E
f
Gauss’ Law
2.
B 0
3.
E
B
t Faradays law
4.
B
J f
E
t Ampere’s Law with Maxwell’s correction
Alternative ways of writing Faraday’s Law
E d
l
ddt
Mutual and self inductance: 2=M21I1 and M21=M12
=LI
Energy stored in a magnetic field: W
1
20
B2
V
d 1
2LI2
1
2
A I dl
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( )
2
/
2
x
K
a h
/
|
2sin
ipx
x
he
ix
h h
x
/ 2
/ 2
|
2/
h a
p h a
dp x p
x a
|
2
sin2
/
p p
K h
ix
x
x aa
/ 2
2
/ 2
ipx
ihx a
edp
e e
a
a a
/
/ 2
( )
sin
ihx a
p
e
c /x
/
/2
2
2
h
h
K
K h
x
.a
/ 2/
/ 2
/
2
aipx
a
ix a
dp e
e e
i
/ix a
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Mechanics Group A. Solutions:
A1.
v
v ,
Since , then it is not inertial. A2. To stop the motion, we need to apply the pulse when the mass arrives at the equilibrium position, where all the potential energy converts onto kinetic energy. Then we have:
212
12
The impulse is given by . To find the time, it is necessary to choose 0, then:
0
, with n an integer.
Thus we get time as:
2 12
A3. Suppose the total kinetic energy at the end of the ramp is , and the radius of both cylinders is , then:
12
12
12
12
With . Then we have:
Then, if we know the relation between and , we can figure out the relation between its velocities.
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A4.
a) The equilibria occur when 0.
4 2 0
There exist three equilibrium points:
0, and
The stability is determined by , then:
12 2
To 0:
2 0
Then, 0 is an unstable equilibrium point.
To :
,
4 0
Then, the stable equilibrium occurs at
b) The frequency of small oscillations is given by:
1
,
2
c) Dimension for and are:
∗ ∗ ∗
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Mechanics Group B. Solutions: B1. Before of thrust:
12
12
ϵ 12
0
After of thrust →
12 2
12
ϵ 12
1
Then,
1 ϵ1 ϵ
1 11 1
2
B2. 1
(a) Equations of motion are given by:
0
Then:
: 1 0
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: cos 0
⇨ cos 0
(b) Yes, is cyclic. The conserved momentum is 1 (c) Hamiltonian is obtained by:
1 ⇨ 1
⇨
Then,
2 1 2 3
H is independent of time, thus energy is conserved. B3. We have the relation between and heat as , where is the constant for this linear relation. Then . According to the conservation of total energy, the gravitational potential energy will be converted into kinetic energy and heat, which is
This can be interpreted as:
sin cos ⇨ sin cos cos
Also
sin1
Thus we get: 1
cos cos
⇨ cos1
cos
⇨coscos 1
cos 1
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B4.
Accor
Then,
rding to the f
we get
c
force balance
:
:
cos2
e, we get:
sin2co
⇨
sin
s
⇨ 2 ar
n2
sin
rccos
n2
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Thermodynamics and Statistics Group A. Solutions: A2. At the solid float. A3. ,
Now, using the relations:
1
And 1
⇨ 1
⇨
A4. A) The Kelvin statement of the second law. “It is impossible to construct an engine that, operating in a cycle, will produce no effect other than the extraction of heat from a reservoir and the performance of an equivalent amount of work”. (Zemanzky-Thermodynamics) B) The Clausius statement of the second law.
G T
P
P1
S
L
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“It is impossible to construct a refrigerator that, operating in a cycle, will produce no effect other than transfer of heat from a lower-temperature reservoir to a higher-temperature reservoir”. (Zemanzky-Thermodynamics) C) The entropy statement of the second law. For any kind of process the entropy of the Universe follows∆ . Always the entropy increase or at least keep constant, but never decrease (Universe is the whole system). In some parts of the system the entropy can decrease, but for the whole system increase or keep constant.
∆ reversible process ∆ irreversible process
(Zemanzky-Thermodynamics)
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Thermodynamics and Statistics Group B. Solutions: B1.
a) At the equilibrium, the two blocks reach the same temperature . For the heat engine we have:
⇨
Also ,
Then we get: 2
b) ∆ ∆ ∆ 0 B2.
⇨ ⇨
1 1
Since , then
1 11
1 11
For limits → 0 and → , we have:
1
B3. (a) No
Cooling of water = melted amount of ice Then,
4186 x1 x20 x334 ⇨ 250.66
(b) ∆ ∆ ∆ ln
∆ 1 x4186 x ln273293
4186x1x20273
10.713
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ElectrSoluti A1. Ca
Case 2
A2.
Then, Now,
ricity and Mions:
ase 1: charg
2: An infinite
, b
the electric
∝ | | ⇨
Magnetism G
e Q at
e, grounded
both have th
field is decr
⇨ decre
Group A.
14
2
plane condu
14 4
he same direc
eased.
eases.
- - - - - - - -
4
uctor is place
4
ction.
14 2
14
116
++++++++
12
ed in the xy-
14
116
32
plane
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A3. We have:
According with the Lorentz force:
Then:
And the charge is positive. A4.
12
and K Then:
12
K 2
k
k3
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ElectrSoluti B1.
(a)
(b)
B2. (a
(b)
No rot(c)
ricity and Mions:
) Cylindricamagnitude
) The AmpeInside (
Outside (
a)
tation of ∙
Magnetism G
al symmetry for the samre loop is co
):
):
⇨
due to |
Group B.
requires Be distance fr
oaxial with th
⇨
⇨
⇨
⇨
41
4
B–field in throm the z–axhe cylinder.
∙
2
2
3 ∙
4
4
he direction xis.
2
2
of and
0
has the samme
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is B3. (a)
No bo (b)
(c)
⇨
s repelled by
und volume
|| ||
alon
∙
y
current, sin
ng axis of cyl
∙
∙
⇨
ce
linder
434
34
0
4
0
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B4. (
(b)
(c) On
(a)
n the surface
⇨
: 0
:
:2
1
1
of the spher
⇨
⇨
⇨
2⇨
2 cos
re, surface ch
,
2
,
2,
0,
ε ∙ 1sin
sin
s 1sin
0 harge densit
, antisotropic
0, 0
0,
,
n
2 sin
ty , no volu
c
0 ↑
0 ↑
0 ↓
1sin
n
ume charge ddensity
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Quantum Mechanics Group A. Solutions:
A1. For photon , then for the electron
80x10 x1.602x102x9.109x10 x 2.998x10
1.003x10 J 6.262
A2. , because of the symmetry of the wave function.
A3.
, , , , , , , , , ,
, 2 ħ 2 ħ 2 ħ Thus, it is not Hermitian A4. (a)
|⟩12
√3| ⟩12| ⟩
⟨|⟩12
√3⟨ |12⟨ |
12
√3| ⟩12| ⟩
⟨|⟩34
14
1
⇨|⟩ is normalized. (b)
| ⟩513
| ⟩1213
| ⟩
|⟨ |⟩| 513
⟨ |1213
⟨ |12
√3| ⟩12| ⟩
1226
36169
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Quantum Mechanics Group B. Solutions:
B1. (a) According to normalization ∗ 1, we get:
1 ⇨
(b)
⟨ |⟩ ⟨ | ⟩⟨ | ⟩ħ
√2 ħ
2ħ
sin√
sin
B2. (a) ħ2
12
(b) Normalization:
⟨|⟩ 1 ⟨12√3
12√3 ⟩
34
Then,
(c) Since → , then 0, √3
(d) ⟨ ⟩ ħ ħ ħ
B3. (a)
2ħ
2x9.109x10 x10x1.602x10 1.055x10
1.6193x10 m
ħ2
∗ ∗ħ
⇨ ħ
9.109x10 x4.0x10 1.6193x10 m x1.055x10
0.462
(b) ħ
and . Then we get:
2
ħ
⇨ ,2
ħ
(c) The boundary conditions are at 0
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, ⇨ ,
2,⇨ 0
(d)
, ⇨ | || |
1
(e)
1%, ⇨ 2ħ
10 51.265
B4. (a) Normalization ⟨|⟩ 1
⇨ 1 ⇨ 12
3
(b)
∗3
1132
(c) is an even function which is symmetrical about 0, then is an odd function which is antisymmetrical.
(d) ⟨ ⟩
(e) ∆ ⟨ ⟩ ⟨ ⟩√