Create assignment, 00224, Homework 7, Mar 06 at 6:45 pm
1
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time.
Charged Particle in a Field 02
29:01, trigonometry, multiple choice,
>
1 min,
fixed.
001
A charged particle is projected with its initial
velocity parallel to a uniform magnetic field.
What is the resulting path?
1.
straight line parallel to the field.
correct
2.
parabolic arc.
3.
circular arc.
4.
straight line perpendicular to the field.
5.
spiral.
Explanation:
The force on a moving charge due to a
magnetic field is given by
~
F
=
q~v
×
~
B .
If
~v
and
~
B
are parallel, then
~v
×
~
B
= 0
.
Hence the force on the particle is zero, and
the particle continues to move in a straight
line parallel to the field.
keywords:
Field Direction
29:01, highSchool, multiple choice,
<
1 min,
fixed.
002
The direction of the magnetic field in a certain
region of space is determined by firing a test
charge into the region with its velocity in
various directions in different trials.
The field direction is
1.
one of the direction of the velocity when
the magnetic field is zero.
2.
the direction of the velocity when the
magnetic force is a maximum.
3.
the direction of the magnetic force.
4.
perpendicular to the velocity when the
magnetic force is zero.
5.
None of these
correct
Explanation:
The magnetic field direction can be deter
mined according to the path of a charge which
moves in the field. Since
~
F
=
q~v
×
~
B ,
the component of velocity along the magnetic
field doesn’t contribute to the magnetic force;
i.e.,
a charge moving along the magnetic field
will keep its motion status. On the contrary,
if the initial velocity in perpendicular to the
magnetic force, there will be a centripetal
force so that the charge will undergo circular
motion.
keywords:
Force on an Electron
29:01,
trigonometry,
numeric,
>
1
min,
wordingvariable.
003
An electron is projected into a uniform mag
netic field given by
~
B
=
B
z
ˆ
k
+
B
x
ˆ
ı
, where
B
z
= 3
.
7 T and
B
x
= 1
.
4 T.
The magnitude of the charge on an electron
is 1
.
60218
×
10

19
C
.
z
x
y
v
= 370000 m
/
s
electron
3
.
7 T
1
.
4 T
B
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Create assignment, 00224, Homework 7, Mar 06 at 6:45 pm
2
Find the direction of the magnetic force
when the velocity of the electron is
v
ˆ
ı
, where
v
= 370000 m
/
s.
1.
b
F
= ˆ
correct
2.
b
F
=

ˆ
3.
b
F
= ˆ
ı
4.
b
F
=
ˆ
k
5.
b
F
=

ˆ
ı
6.
b
F
=

ˆ
k
7.
b
F
=
1
√
2
‡
ˆ
k
+ˆ
ı
·
8.
b
F
=
1
√
2
‡
ˆ
k

ˆ
ı
·
9.
b
F
=
1
√
2
‡
ˆ
ı

ˆ
k
·
Explanation:
Let :
q
= 1
.
60218
×
10

19
C
,
B
z
= 3
.
7 T
,
and
B
x
= 1
.
4 T
.
Basic Concepts:
Magnetic force on a mov
ing charge is given by
~
F
=
q~v
×
~
B .
Solution:
~
B
= (3
.
7 T)
ˆ
k
+ (1
.
4 T) ˆ
ı
v
= (370000 m
/
s) ˆ
ı
for the electron.
Find:
The vector expression for the force on
the electron. This solves both part 1 and part
2.
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 Spring '10
 Avram
 Physics, Electron, Charge, Work, Magnetic Field, Electric charge, Magnetic Force Directions

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