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Practice Exam 2
PHY 2140
Please print your name here
Row:
Seat:
Please print your student number here
Instructions:
1. Do all the questions. You must show your work for partial credit. I must be able
to understand what you have done while I am grading the exam – not when you
explain it to me after the exam is graded and returned.
2. For each problem:
(a) write down any formula(s) used
(b) justify why you used that particular formula(s)
(c) show your work!
3. The formula sheet is on the last page of the exam. You may detach it from the rest
of the exam.
NAME
1. What is the current through the 3.00 Ω resistor?
I3
a.
b.
c.
d.
e.
1.50 A
2.00 A
2.50 A
3.00 A
3.50 A
1Ω
3Ω
12 V I2
5Ω
3Ω
I1
8Ω
12 V
2. In the series RC circuit shown, what is the maximum charge on the capacitor after the
switch is closed? (note MΩ = x 106 Ω )
a.
b.
c.
d.
e.
0C
12 C
36 μC
48 μC
144 C
4MΩ
12 V
3. Kirchhoff’s junction rule is a statement of conservation of:
a.
b.
c.
d.
e.
angular momentum.
energy.
charge.
linear momentum.
time.
3μF
NAME
4. At what distance from a long straight wire carrying a current of 6.0 A is the magnetic
field due to the wire equal to the strength of the earth’s field, 5.0 x 10-5 T?
a.
b.
c.
d.
e.
0.0024 m
0.024 m
0.24 m
2.4 m
24 m
5. At what speed v should the bar in the figure be moved to produce a current of 1A in the
resistor? Assume B = 2.50 T into the page, R = 6.0 Ω and the length of the bar is 1.50 m.
a.
b.
c.
d.
e.
Zero
0.625 m/s
1.00 m/s
1.60 m/s
2.65 m/s
v
R
Bin
I
6. How would the self-inductance of a coil be changed if half of the length of wire were
wound around the same cylinder? It would be:
a.
b.
c.
d.
e.
the same.
doubled.
quadrupled.
halved.
quartered.
7. A cube with an edge of length l = 0.05 m is positioned as shown. There is a uniform
magnetic field throughout the region that has components Bx = 5 T, By = 4 T and
Bz = 3 T. What is the flux through the shaded face of the cube?
B
z
a.
b.
c.
d.
e.
Zero
0.0075 T·m2
0.01 T·m2
0.0125 T·m2
0.20 T·m2
x
y
NAME
8. A hanging Slinky toy ( a tight coil of spring steel ) is attached to a powerful battery and a
switch. When the switch is closed so that current suddenly flows through the Slinky, the
slinky:
a.
b.
c.
d.
e.
vibrates.
compresses.
expands.
rotates.
does nothing.
9. What is the direction of the current induced in the resistor when the current in the long,
straight wire in the figure below (1) decreases rapidly to zero and (2) is then made to flow
in the opposite direction?
a.
b.
c.
d.
e.
(1) left to right and (2) right to left.
(1) left to right and (2) left to right.
(1) right to left and (2) right to left
(1) right to left and (2) left to right
There is no current in the resistor.
R
I
10. An 8 turn coil encloses a triangular area with a height of 30 cm and base of 40 cm as
shown. The coil lies in the plane of the page and carries a current of 6.00 A flowing
clockwise around it. If the coil is in a uniform magnetic field of 2.00 x 10-4 T, directed
towards the left of the page, what is the magnitude of the torque on the coil.?
a.
b.
c.
d.
e.
Zero
5.76 x 10-4 N·m
1.15 x 10-3 N·m
5.76 N·m
11.5 N·m
I
B
30 cm
40 cm
NAME
11. A particle with a charge of +2.0 microcoulombs and a kinetic energy of 0.090 J is fired
into a uniform magnetic field of magnitude 0.10 T. If the particle moves in a circular
path with a radius of 3.0 m, determine its mass. Please show your work in solving this
problem.
12. Find the equivalent resistance between points a and b. Please show your work in solving
this problem.
5Ω
20 Ω
9Ω
8Ω
a
2Ω
b
KE =
1 2
mv
2
P = IΔ V
F = qvB sin θ
mv
r=
qB
ΔΦ
E = −N
Δt
F = ma
(ΔV )2
v2
r
ΔV = IR
Req = R1 + R2 + …
1
1
1
=
+
+…
Req R1 R2
F = BI sin θ
μ I
B= 0
2πr
τ = F sin θ
μ 0 NI
τ = NBIAsin θ
E= B v
E = NABω sin (ω t )
P = I 2R =
ω = 2πf
PE =
a=
1 2
LI
2
g = 9.8 m/s2
ε0 = 8.85 x 10-12 C2/Nm2
me = 9.11 x 10-31 Kg
R
E = −L
ΔI
Δt
τ = RC
B=
L=
NΦ
I
Q = C ΔV
ke=8.99 x 109 Nm2/C2
1 kWh = 3.60 x 106 J
electron charge = 1.60 x 10-19 C
Area of triangle = ½ base x height
Φ = B⊥ A = BA cosθ
Emax = NABω
L=
μ0 N 2 A
τ=
1 eV = 1.6 x 10-19 J
μ0 = 4π × 10−7 Tm/A
1 hour = 3600 sec
L
R