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29. (a) If
v
is the speed of the positron then
v
sin
φ
is the component of its velocity in the
plane that is perpendicular to the magnetic field. Here
is the angle between the velocity
and the field (89°). Newton’s second law yields
eBv
sin
=
m
e
(
v
sin
)
2
/
r
, where
r
is the
radius of the orbit. Thus
r
= (
m
e
v
/
eB
) sin
. The period is given by
( )
()
31
10
19
29
.
1
1
1
0k
g
2
2
3.58 10
s.
sin
1.60 10
C 0.100T
e
m
r
T
ve
B
−
−
−
π×
π
π
==
=
=
×
×
The equation for
r
is substituted to obtain the second expression for
T
.
(b) The pitch is the distance traveled along the line of the magnetic field in a time interval
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 Spring '08
 Any
 Physics

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