ch32 - Chapter 32 MAXWELL'S EQUATIONS MAGNETISM AND MATTER...

Chapter 32: MAXWELL’S EQUATIONS; MAGNETISM AND MATTER
1. Gauss’ law for magnetism:
A. can be used to fi nd
n
B due to given currents provided there is enough symmetry
B. is false because there are no magnetic poles
C. can be used with open surfaces because there are no magnetic poles
D. contradicts Faraday’s law because one says Φ
B
= 0 and the other says E = − d Φ
B
/dt
E. none of the above
ans: E
2. Gauss’ law for magnetism tells us:
A. the net charge in any given volume
B. that the line integral of a magnetic fi eld around any closed loop must vanish
C. the magnetic fi eld of a current element
D. that magnetic monopoles do not exist
E. charges must be moving to produce magnetic fi elds
ans: D
3. The statement that magnetic fi eld lines form closed loops is a direct consequence of:
4. A magnetic fi eld parallel to the x axis with a magnitude that decreases with increasing x but
does not change with y and z is impossible according to:
A. Faraday’s law
B. Ampere’s law
C. Gauss’ law for electricity
D. Gauss’ law for magnetism
E. Newton’s second law
ans: D
5. According to Gauss’ law for magnetism, magnetic fi eld lines:
A. form closed loops
B. start at south poles and end at north poles
C. start at north poles and end at south poles
D. start at both north and south poles and end at in fi nity
E. do not exist
ans: A
Chapter 32: MAXWELL’S EQUATIONS; MAGNETISM AND MATTER 475

6. The magnetic fi eld lines due to an ordinary bar magnet:
7. Four closed surfaces are shown. The areas A
top
and A
bot
of the top and bottom faces and the
magnitudes B
top
and B
bot
of the uniform magnetic fi elds through the top and bottom faces
are given. The fi elds are perpendicular to the faces and are either inward or outward. Rank
the surfaces according to the magnitude of the magnetic fl ux through the curved sides, least
to greatest.
. . .. .
. .
. . . . . . .
.
.
. . . . ... .. .
.
. .
A
top
= 2 cm
2
B
top
= 2 mT, inward
A
bot
= 4 cm
2
B
bot
= 2 mT, outward
1
.. . ....
. . . . . . . .
.
.
.. .
. . . ...
.
. .
A
top
= 2 cm
2
B
top
= 2 mT, inward
A
bot
= 4 cm
2
B
bot
= 6 mT, outward
2
..
. .. .
. . . . . . . .
.
..
. .. .
.
.
.
.
.
A
top
= 2 cm 2
B
top
= 3 mT, inward
A
bot
= 2 cm 2
B
bot
= 3 mT, outward
3
.. . ....
.
. . . . . . . . . .
.
.. . ....
.
.
.
.
.
A
top
= 2 cm 2
B
top
= 3 mT, inward
A
bot
= 2 cm 2
B
bot
= 2 mT, outward
4
476 Chapter 32: MAXWELL’S EQUATIONS; MAGNETISM AND MATTER