Download Exam 3

Phys 121 Exam 3
__________________________________________________________________________________________
j = (ne) vd
j = i/A V = iR
P = iV
P = i2R = V2/R series: Req = R1 + R2+..Rn parallel: Req= (1/R1+1/R2+..1/Rn)-1
RC-circuit: charging: Q = Q(1-e-t/RC),
discharging:
Q = Q0 e-t/RC,
Fm = qvxB
Fe = qE
 = xB
 = NiA
Bsolenoid = 0in
VC = V (1-e-t/RC),
i = i0 (e-t/RC),
Fm = iLxB
B wire, out = 0i/2R
Flux:  = BA
i = i0 (e-t/RC),
Vc = V0 (e-t/RC),
v = E/B
qΔ =Kf-KI
VR = i0 R (e-t/RC),
VR = i0 R (e-t/RC),
K=½mv2
B wire, in = (0i/2R2)r
emf = -d/dt emf = (2-1)/t
qvB = mv2/R
Barc = 0i/4R
emfmot = BLv
R=mv/qB
Bloop = 0i/2R
emfmax = NAB
0 = 1.26x10-6 Tm/A
e = 1.6x10-19 C
me = 9.11x10-31kg
1 Two identical batteries of emf E=3V and internal resistance r=0.4- are connected in parallel then connected in series
with R=2- resistor. The current in the 2- resistor is:
A) 1.36 A
B) 1.85 A
C) 2.13 A
D) 2.95 A
E) 3.71 A
2. The power dissipated in the 2- resistor (in problem 2) is
A) 3.7 W
B) 6.9 W
C) 9.1 W
D) 17.3 W
E) 27.4 W
3. What is the current in a R = 0.5 resistor connected to a battery that has a r 0.3 - internal resistance when the
potential drop across the terminals of the battery is E 9-V when measured without any load?
A) 11
B) 18
C) 30
D) 48
E) none
4. For the RC circuit shown ( R = 1M, C = 5 F and  = 30 V) find the potential
difference across the resistor 10 sec after the switch is closed.
A. 0.5 V
B. 1.5 V
C. 3.0 V
D. 3.5 V
E. 4.0 V
1
5. A portion of a circuit is shown, with the values of the currents given for some
branches. What is the direction and value of the current i?
A) 6 up
B) 6 down
C) 1 up
D) 1 down
E) none
6. A particle with positive charge q .3 10 6 -C is a distance d 1.5 10 2 -m from a long straight wire that
carries a current i 5-A. The particle is traveling with speed v = 1000 m/s perpendicular to the wire. What
are the direction and magnitude of the force on the particle if it is moving away from the wire? (in N)
1.0.10-8
1.0.10-8
2.0.10-8
2.0.10-8
2.0.10-7
A)
B)
C)
D)
E)
up
down
up
down
up
7. An electric generator consists of N 500 turns of wire formed into a rectangular loop a = 0.05 m by b = 0.03 m placed
entirely in a uniform magnetic field with magnitude B o 2.5 -T. What is the maximum value of the emf produced when the
loop is spun at 
1000 rev/min about an axis perpendicular to B?
A)
B)
C)
D)
E)
196.0
124.1
55.3
39.2
20.3
8.
A)
B)
C)
D)
E)
In the formula F = qvxB:
F must be perpendicular to v but not necessarily to B
F must be perpendicular to B but not necessarily to v
v must be perpendicular to B but not necessarily to F
all three vectors must be mutually perpendicular
none of the above
A positive particle (a proton) with charge 1.6.10-19C and mass 1.67x10-27 kg is moving with a velocity v=2.105 m/s in the
positive z direction. A magnetic field B = 125.10-3 T is pointing in the positive y direction .
9. Find the force acting on the particle.
A)
B)
C)
D)
E)
4 x 10-15 N, in the positive x-direction
4 x 10-15 N, in the negative x-direction
1.6 x 10-19 N, in the positive z-direction
1.6 x 10-19 N, in the negative z-direction
zero
10. Find the frequency of proton circular motion.
2
A)
B)
C)
D)
E)
1.9 MHz
1.2 MHz
0.5 MHz
0.2 MHz
0.1 MHz
11. The magnetic field B = 0.5j is acting on proton moving in xy plane with velocity
v =105i +105j (in m/s). Find the force acting on the proton.
A)
B)
C)
D)
E)
8 x 10-15 N, in the positive z-direction
8 x 10-15 N, in the negative z-direction
1.6 x 10-19 N, in the positive y-direction
1.6 x 10-19 N, in the negative y-direction
zero
12. Magnetic field B = 1 T goes out of the plane of the page. A straight wire carries a current 1 A from right to left. Find
the direction of force acting on the wire.
A)
B)
C)
D)
E)
out of the page
into the page
left, in the plane of the page
right, in the plane of the page
up, in the plane of the page
13. Two circular coils of equal radius 2 cm are placed several centimeters apart. If viewed from left, the current in the both
loops is clockwise. The direction of magnetic field along the axis passing through the loops' centers and halfway
A)
B)
C)
D)
E)
is to the right.
is to the left.
is oscillating.
zero
depends on the distance between coils
14.
The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r,
and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic
fields they produce at C, least to greatest.
A)
1, 2, 3
B)
3, 2, 1
C)
1, 3, 2
D)
2, 3, 1
E)
2, 1, 3
3
Workout problems:
1.For the circuit shown find the magnitude of the current through each of the resistor if E=24 -V
and R1 = 5  R2 = 10  and R3 = 15 
2. The wire shown in fig. carries current I = 5 A. If the R = 20 cm what net magnetic field B
( magnitude and direction) is produced at the center C of the semicircle by the entire wire?
4