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1
5
6
A cosmic-ray proton approaches
Earth vertically at the equator,
where the horizontal component
of Earth¡¯s magnetic field is
3.5 10 T. If the proton is
moving at 3.0 10 m/s, what
is the ratio of the m
?
?
?
agnetic
force to the gravitational force
on the proton?
Solution
MAGNETIC FORCE ON A MOVING CHARGED PARTICLE
2
3
Let be the Magnetic Force &
be the Gravitational Force,
then
(1)
(2)
where is the mass of the Proton
B
G
B
G p
p
F
F
F quB
F m g
m
? ? ? ?
? ? ? ?
19 6
5
27
2
18
9
27
2
9
2
Now,
(1.6 10 ) (3.0 10 )
(3.5 10 )
(1.67 10 )(9.8 )
16.8 10 . .
. .
1.03 10
.
16.37 10
1.03 10
. . . . .
( 1)
. . . .
B
G
m
X C X X X
s
F X T
m
F X kg
s
m
X C T
C T s
s X
kg m kg
X
s
X
C T s C kg s C A s
kg A s kg A s A s
?
?
?
?
?
?
? ?
?
? ? ? ?

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Ratio Fb & Fg.doc

  • 1. 1 5 6 A cosmic-ray proton approaches Earth vertically at the equator, where the horizontal component of Earth¡¯s magnetic field is 3.5 10 T. If the proton is moving at 3.0 10 m/s, what is the ratio of the m ? ? ? agnetic force to the gravitational force on the proton? Solution MAGNETIC FORCE ON A MOVING CHARGED PARTICLE
  • 2. 2
  • 3. 3 Let be the Magnetic Force & be the Gravitational Force, then (1) (2) where is the mass of the Proton B G B G p p F F F quB F m g m ? ? ? ? ? ? ? ? 19 6 5 27 2 18 9 27 2 9 2 Now, (1.6 10 ) (3.0 10 ) (3.5 10 ) (1.67 10 )(9.8 ) 16.8 10 . . . . 1.03 10 . 16.37 10 1.03 10 . . . . . ( 1) . . . . B G m X C X X X s F X T m F X kg s m X C T C T s s X kg m kg X s X C T s C kg s C A s kg A s kg A s A s ? ? ? ? ? ? ? ? ? ? ? ? ?