Physics 121
Fall 2005
Physics constants:
Final Exam
1.6 10
qe
19
-C
Name _______________________________
9.11 10
me
31
i
A
A x i
B x j
A z k
B
A x i
B x j
A z k
A
Forces in magnetic field: F B q  v B
centripetal force F m
v
dB
m v
q B
r
 o  i 
4 R
k
Bx By Bz
 o  L i a  i b
i L B
F
2 d
FB
T
2   m
q B
1
f
2   f

T

N i A

 o  i ds r
3
4
r
at the center of a full circle: B
 o i
2 R
 o i
2R
at the center of a fraction of a circle:
inside ideal solenoid B  o  in where n =
 o N  i A

3
2
z
 o i o N 1

r
2
magnetic flux through area A  B
d B
Faraday's Law: 
P
Fv
E
B l v
i
V
P
di
L
dt
for N turns 
2
i R
L
R
N B
RL circuits :
L
Energy U B
1  2
Li
2
i
 L
inside toroid:
Bd A
 L
dt
B
Amper's Law
number of turns per unit length; on the axis of a current loop: B( z)
B

 B
Magnetic Field by: straight infinite wire: B
B
7
Ax Ay Az
B
magnetic dipole moment
U(  )
Magnetic potential energy
Biot-Savart Law
4   10
 o
R
N i a  b  B sin(  )

j
27
2
Charge in magnetic field
Torque
1.673 10
-kg m p
L
R
i
E
R
1
N
d B
dt
2
 o n A l
e
t
t
 L
 L
or
i
E
R
e
L
N B
i
Physics 121
Fall 2005
Final Exam
Name _______________________________
As a student at NJIT I will conduct myself in a professional manner and will comply with the provisions of the
NJIT Academic Honor Code. I also understand that I must subscribe to the following pledge: On my honor, I
pledge that I have not violated the provisions of the NJIT Academic Honor Code.
1 A beam of ions passes through a pair of crossed electric and magnetic fields along a straight line. The
magnitude of electric field E is 600000 N/C and the magnitude of magnetic fields B is 0.003 T. What is the
speed of the ions?
A) 2.108 m/s
B) 1.8*103 m/s
C) 5.10-9 m/s
D) 4.1016 m/s
E) 2 m/s
2 An electron in a vacuum is first accelerated by a voltage of 11000 V and then enters a region in which there
is a uniform magnetic field of 0.1 T at right angle to the direction of the electron's motion. What is the force on
the electron due to the magnetic field?
A) 1.1.105 N
B) 1.1.103 N
C) 0.097 N
D) 4.1.10-7 N
E) 1*10-12 N
3. A copper bar is moving from left to right while its axis and its velocity are maintained
perpendicular to a magnetic field. If the rod is charged as in fig what is the direction of the
magnetic field? (the magnetic field is perpendicular to the velocity).
A). into the plane of the paper
B). out of the plane of the paper
C) South
D) to answer the question the figure must show a battery
E) It is impossible to have + and - charges separated in the copper bar.
4. A current of 2.7 A flows in a straight wire segment of length (3 cm) i + (4 cm) j in a uniform
magnetic field B of (1.3 T) i. Find the magnitude of the force on the wire.
A) 0.14 N
B) 0.105 N
C) 0.176 N
D) 0.013 N
E) 3.10-3 N
5. The wire is carrying a current I = 2A. Find the
magnitude of the magnetic field B at point O due to
a current-carrying wire shown in the figure, where
the semicircle has radius r = 35cm, and the straight
parts to the left and to the right extend to infinity.
A) 0.18 mT into the page
B) 0.18 mT out of the page
C) 1.8 mT into the page
D) 1.8 mT out of the page
E) 7.2 mT South
Physics 121
Fall 2005
Final Exam
Name _______________________________
6. The rectangular loop in fig is pivoted about the y axis and carries a current of 10 A in the direction
indicated. If the loop of size a = 20 cm and b = 40 cm is in a uniform magnetic fied of magnitude 0.2
T, parallel to the x -axis, find the torque required to hold the loop in the
position shown if angle  is 370.
A) 0.22 Nm
B) 0.16 Nm
C) 0.13 Nm
D) 0.096 Nm
E) 0.062 Nm
7. Two long, parallel wires are separated by a distance of 0.3 m, as shown in fig. The currents I 1 and I2 have
the directions shown. Calculate the magnitude and direction of the force exerted by I1 wire on a 1 m length of
the I2 wire.
A) 3.0 mN into the page
B) 0.010 mN out of page
C) 0.010 mN South
D) 3.0 mN North
E) 3.0 mN East
8. The long, straight wire AB carries a current I of 20 A. The rectangular loop whose
long edges are parallel to the wire carries a current of 10 A. Find the magnitude and
direction of the resultant force exerted on the loop by the magnetic field of the wire.
A) 0.72 mN West
B) 0.062 N West
C) 0.0056 N West
D) 0.72 mN East
E) 0.062 N East
9. The long, straight wire AB carries a current I of 20 A. The position and size of
a loop is shown in figure. What is the magnetic flux  B through the loop?
A) 1.85.10-6 Wb
B) 5.1.10-4 Wb
C) 5.6.10-4 Wb
D) 5.6.10-3 Wb
E) 0.14 Wb
Physics 121
Fall 2005
Final Exam
Name _______________________________
10. Two long, parallel wires perpendicular the xy plane, each carrying a current I = 7A
but in opposite directions. Calculate the magnitude of magnetic field B at point P
if a = 3 cm
A) 1.9*10-5 T
B) 3.2*10-5 T
C) 3.8*10-5 T
D) 6.6*10-5 T
E) 8.2*10-5 T
11. The rectangular loop in fig is pivoted about the y axis. If the loop of
size a = 20 cm and b = 40 cm is in a uniform magnetic field B of
magnitude 0.2 T, parallel to the x -axis, and rotates with angular
frequency  = 1500 rev/min find the amplitude of electromotive force E
induced in the frame.
A) 2.5 V
B) 3.2 V
C) 0.016 V
D) 24 V
E) 0.062 V
12. A metal rod of resistance R = 12- is forced to move with constant velocity v = 60 cm/s along two
parallel metal rails separated by d = 45 cm and connected at one end (see fig). A magnetic field of
magnitude B = 0.35 T points out of the page. What electromotive force is generated in the rod?
A) 7.9.10-3 V
B) 0.094 V
C) 3.15 V
D) 15.5 V
E) 1.13 V
13. What is the equivalent inductance of the circuit if L 1 = 15 mH, L2 = 30 mH, L3 = 50 mH,
and L4 = 25 mH.
A) 120 mH
B) 85 mH
C) 62 mH
D) 27 mH
E) 19 mH
14. In the figure E = 90V, R1 = 20, R2 = 30, and R3 = 60. The switch S is closed at time t = 0.
What is the current i1 immediately after switch S is closed?
A) 4.5 A
B) 3 A
C) 1.5 A
D) 1.125 A
E) 0.82 A
Physics 121
Fall 2005
Final Exam
Name _______________________________
15. Fifty turns of wire are wrapped into a coil 0.32 m in diameter and length of 30 cm. The coil is
connected to a 12 V battery. If the total resistance of the coil is 0.9, what is the magnetic field in the
center of the coil?
A) 1.3 mH
B) 1.7 mH
C) 2.1 mH
D) 2.8 mH
E) 4.7 mH
16
A)
B)
C)
D)
E)
What is the magnetic moment of a 12.5 cm diameter coil of 150 turns when it carries a current of 75 mA?
0.11 Am2
0.22Am2
0.33 Am2
0.44 Am2
0.55 Am2
17. A copper wire (ab) is wound around a wooden rod (see fig.).
Another wire (cd) is wound on top of it and connected to a resistor R.
question one What is the direction of current in R if a current flowing
from a to b is increasing?
question two What is the direction of current in R if a current flowing
from b to a is decreasing?
A) one: dc two: dc
B) one: dc two: cd
C) one: cd two: dc
D) one: cd two: cd
E) none of these
18. At the instant of time t = 0 the current from A to C in the figure is 30 A and is decreasing at the rate
of 10 A/s. What is the electric potential difference between A and C at t = 0?
A) 3 V
B) 18 V
C) 21 V
D) 24 V
E) 28 V
Physics 121
Fall 2005
Final Exam
Name _______________________________
1A 2E 3A 4A 5C 6D 7C 8A 9A 10B 11A 12B 13C 14D 15D 16E 17D 18B