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Practice Final Exam
PHY 2140 – Sp/Su 2007
1.
How many 100 W lightbulbs can you use in a 120 V circuit without tripping a 15 A circuit
breaker.
2.
Find the charge on the 4 F capacitor in the following circuit.
8 F
8 F
4 F
4V
3.
A hydrogen atom initially in its ground state (n = 1) absorbs a photon and ends up in the state for
which n =3. What is the wavelength of the absorbed photon?
4.
What is the current through the 8.00  resistor?
2
2
8
2
4
12 V
5.
A cube with an edge of length l = 0.04 m is placed in a uniform magnetic field throughout the
region that has components Bx = 0, By = 4 T and Bz = 3 T. Find the flux through the top face of the
cube.
z
x
y
6.
7.
The half-life of an isotope of phosphorus is 14 days. If a sample contains 3.541016 such nuclei,
what is its activity?
A cylindrical piece of insulating material is placed in an external electric field, as shown. The net
electric flux passing through the surface of the cylinder is
8.
Light with a wavelength of 4.210-7 m is used to determine the position of an electron to within
one wavelength. What will be the resulting uncertainty in the electron’s velocity?
9.
Determine X in the following reaction:
21
10
24
Ne  ZA X  12
Mg  01n (use the table below if
necessary).
10. An astronaut at rest on Earth has a heartbeat rate of 60 beats/min. When the astronaut is traveling
in a spaceship at 0.80 c, what will this rate be as measured by an observer at rest on Earth?
11. Determine the amount of energy released in the fusion reaction: 1 H  1 H  2 He  
1
2
3
12. A simple circuit consists of a resistor R, an inductor L, a battery and a switch that is initially open
but then thrown closed. Immediately after the switch is thrown closed, the current in the circuit is
R

13. An electron moves in a circular path perpendicular to a constant magnetic field. If the angular
momentum of the electron about the center of the circle is 4.0010-25 J·s and the radius of its path
is 10 cm, determine the magnitude of the magnetic field. ( Hint: the angular momentum of the
electron is L = mvr) Please show your work in solving this problem.
14. What is the speed of a particle if its kinetic energy equals 80% of its rest energy? Please show
your work in solving this problem.
15. An inductor and a resistor are connected in series. When connected to a 60 Hz, 100 V source, the
voltage drop across the resistor is found to be 30 V and the power delivered to the circuit is 9 W.
What is the value of the resistor? Please show your work in solving this problem.
KE 
1 2 p2
mv 
2
2m
F  ma
P  IV
P  I 2R 
F  qvB sin 
mv
r
qB
I max
I rms 
2
Vrms 
V 2
R
F  BI sin 
 I
B 0
2r
2
  F sin 
 0 NI
  NBIA sin 
XC 
VL , rms  I rms X L
2

t
  2f
1 2
LI
2
E
v
B
E B
E2
cB 2
P  max max  max  max
2 0
2 0 c 2 0
tan  
V  IZ
EB v
E  L

L
X L  2fL
XL  XC
R
Pav  I rms Vrms cos 
N
I
  RC
Q  C V
E
c
B
c  f
t  t P
L  LP 
E  mc 2
p  mv
KE  mc 2  mc 2
En  nhf
KEmax  hf  
maxT  0.2898 102 m  K
PE 

h
h

p mv
    0 
a0 
h
(1  cos  )
me c
2
mke2
2
me k e Z 2 e 4  1 
 2
2 2
n 
ln( 2) 0.693




xp 
E
h
4
hc

Ei  E f  E  hf
En  
r  r0 A1 / 3
T1 / 2
E  mc 2
  2f
c  f
  B A  BA cos 
1
2 f C
E  NAB sin t 
I
t
V  IR
1
1
1



Req R1 R2
B
VC ,rms  I rms X C
v2
r
Req  R1  R2  
VR ,rms  I rms R
Vmax
Z  R2  X L  X C 
E  N
a
h
4
Compton wavelength:
h
 0.00243 nm
me c
E t 
 1
1 
 RH  2  2 
n

ni 
 f
N
R
 N
t
1
mvr  n
Emax  NAB
L
0 N 2 A

L

R
f 
 
1
2 LC
1
1  v2 c2
E 2  p 2c2  m2c 4
v AB 
v AC  vCB
v v
1  AC 2 CB
c
min 
hc
eV
2d sin   m
( m  1, 2,3, )
En  
Z2
(13.6 eV)
n2
N  N 0 e  t
r  n 2 a0 / Z
v
A
x f  xi
a
t f  ti
Ax  Ay
2
W  ( F cos  ) s
KE 
 E  EA cos 
Ax
1 2
mv
2
Ax  A cos 
E
2
VB  VA  Ed
F
V  ke
q
r
1
1
1



Ceq C1 C 2
A
d
Fx = m ax
Fy = m ay
Wnet = KEf - KEi
KEf +PEf = KEi + PEi
W  PE
PE  k e
P  I 2R 

A
I
   0 1   T  T0 
V 2
R
g = 9.8 m/s2
1 eV = 1.6 x 10-19 J
1 kWh = 3.60 x 106 J
c = 3.00 x 108 m/s
h = 6.63 x 10-34 J s
1 u = 931.5 MeV/c2
RH =1.097   m-1
I  nqv d A
r2
q1 q 2
r
Q
t
R  R0 1   T  T0 
ke 
PE  qVB  VA 
Q  CV
energy 
P  IV
1
circle, cylinder:
4 0
A  r 2 ,V  r 2 l
electron charge = 1.60 x 10-19 C
For an electron: mec2=511 keV
mp = 1.67 x 10-27 Kg
a0 = 0.0529  9 m
r0 = 1.2  15 m
1
1
1
0
H
Mass (u)
1.007825
n
1.008665
2
1
3
1
3
2
H
2.014102
H
3.016049
He
3.016029
4
2
238
92
He
U
1
2
C V 
2
V  IR
     Tm/A
ke = 8.99 x 109 Nm2/C2
 = 8.85 x 10-12 C2/Nm2
1 hour = 3600 sec
me= 9.11 x 1031 kg
  1.05  10 34 J s
1 u = 1.66  27 kg
Power Prefix Symbol
10-12
picop
10-9 nanon
-6
10 micro
-3
10
millim
10-2 centic
3
10
kilok
106 megaM
109
gigaG
q
C eq  C1  C 2  
1
Q2
energy  QV 
2
2C
R
1 2
at
2
x  v0 t 
E  ke
q0
Ay  A sin 
v  v0  at
F  qE
q1 q 2
C   0
Ay
v v
x 0
t
 2 
2
r
t f  ti
tan  
2
v 2  v0  2ax
F  ke
v f  vi
4.002602
238.050784