Download PHYS2424 - SPRING 2000

PHYS2424 - FALL 2000
EXAM II - Part 1
NAME ______________________________________
SS# _________________________________________
I.
Multiple Choice
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(40 pts)
II.
Maxwell's Eqt.
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(32 pts)
III.
Drawings
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(15 pts)
IV.
Units
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(18 pts)
V.
Fill in the Blank
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(24 pts)
VI.
Short Answer
__________________________________ (8 pts)
________________________________________________________________________
Total Part I
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(137 pts)
Total Part II
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(200 pts)
Exam Total & Grade
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I.
Multiple Choice Problems ( 4 points each )
1.
How is the direction of propagation of an electromagnetic wave oriented relative
to the associated E and B fields?
2.
a)
parallel to both E and B
b)
perpendicular to both E and B
c)
parallel to E, perpendicular to B
d)
parallel to B, perpendicular E
In the circuit shown below, the switch is closed. Which of the following
statements best describes the voltage across the resistor as measured by the DC
voltmeter immediately after the switch is closed?
Switch
R

+
DC
Meter
-
a)
Zero because there is no battery in that part of the circuit
b)
Negative
c)
Positive
d)
Zero because of Lenz's Law
3.
4.
The wavelength of an electromagnetic wave of frequency 1.0x1014 Hz in free
space is
a)
3.0 m
b)
1.0 nm
d)
1.0 km
e)
None of these.
c)
3.0 mm
At a particular instant, a proton experiences a force in the +z direction
while traveling in the uniform magnetic field shown below. What
direction is the electron traveling at this instant?
y
+
B
x
F
z
a)
-z direction
b)
-y direction
d)
+x direction
e)
None of these.
c)
-x direction
5.
6.
7.
Which condition of motion must be met with regard to a charged particle if it is in
the process of emitting electromagnetic radiation?
a)
moves at constant velocity
b)
accelerates
c)
moves at the speed of light
d)
moves parallel to a uniform magnetic field
A particular RL circuit has a time constant of 10.0 s. What fraction of
the maximum voltage across the inductor will be present 25.0 s after a DC
current starts flowing through the inductor.
a)
0.082
b)
0.918
d)
0.330
e)
None of these
c)
0.670
A conducting loop lies in the plane of this page and carries a counter clockwise
induced current. Which of the following could be true?
a)
A constant magnetic field is directed into the page.
b)
A constant magnetic field is directed out of the page.
c)
An increasing magnetic field is directed into the page.
d)
A decreasing magnetic field is directed into the page.
e)
None of these.
8.
9.
10.
The inductance of a coil is 8.00 H and the current through the coil is
5.0 A. If the current is uniformly reduced to 2.0 A in 4.00 milliseconds,
what is the average emf induced in the coil?
a)
6,000 V
b)
1,500 V
d)
10,000 V
e)
None of these
c)
8000 V
Two identical bar magnets are dropped from equal heights. Magnet A is dropped
from above bare earth, whereas magnet B is dropped from above a metal plate.
Which magnet strikes first? (neglect air friction)
a)
Magnet A
b)
Whichever has the N pole toward the ground
c)
Magnet B
d)
Whichever has the S pole toward the ground
e)
Both strike at the same time
According to Maxwell's equations, magnetic field circulation can be caused by
a)
capacitance
b)
c)
time-varying magnetic field d)
e)
none of these
a net charge
time-varying electric field
II.
Maxwell's Equations ( 4 points each )
A.
Write Maxwell's equations in the most general manner in integral form:
1)
Ampere-Maxwell Law
2)
Gauss' Law of Electrostatics
3)
Gauss' Law of Magnetism
4)
Faraday's Law of Magnetic Induction
B.
Write Maxwell's equations in the most general manner in differential form:
1)
Ampere-Maxwell Law
2)
Gauss' Law of Electrostatics
3)
Gauss' Law of Magnetism
4)
Faraday's Law of Magnetic Induction
III.
Drawings (3 pts each except #3 which is worth 6 pts)
1.
Draw the magnetic field lines for the perfect toroid whose cross sectional view is
shown below:
2.
Draw the direction of the current flowing through the loop to produce the
magnetic field lines shown in the diagram.
3.
Shown below is a picture from a cloud chamber in which three particles (A, B,
and C) are created. Given that an external magnetic field is directed out of the
page as shown in the diagram, you are to determine whether each particle is
positive, negative, or neutral and fill in the appropriate blank.
A: ____________________
B: ________________________
C: ____________________
A
B
C
4.
Draw the magnetic field lines for an infinite wire with current flowing out of the
page as shown in the diagram below.
IV.
Fill In The Appropriate Units (3 pts each)
1.
Wavelength
2.
Magnetic Flux _____________________________________
3.
Inductance
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4.
Frequency
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5.
Magnetic Field _____________________________________
6.
Time Constant _____________________________________
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V.
Fill in the Blank (3 pts each)
1.
How many Tesla is 0.5 Gauss?_____________________________________
2.
Write the Biot-Savart Law
3.
Write Faraday's Law ____________________________________________
4.
Write the Lorentz Force Law for magnets _______________________________
5.
Write the equation that defines a magnetic moment _____________________
6.
The magnitude of the magnetic moment due to the spin of an electron is called the
______________________________________
__________________________________________________________________
7.
Write Stoke's Theorem
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8.
Write the formula for determining the energy stored in the magnetic field of an
inductor
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VI.
Short Answer (4 pts each)
1.
Can a charged particle move through a magnetic field without experiencing any
force? If so, how? If not, why not?
2.
A sheet of copper is placed between the poles of an electromagnet with the
magnetic field perpendicular to the sheet. When it is pulled out, a considerable
force is required, and the force required increases with speed. Explain.