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E
qz
zR
=
+
4
0
22
32
π
ε
c
h
/
where
q
is the charge on the ring and
R
is the radius of the ring (see Eq. 2216). For
q
positive, the field points upward at points above the ring and downward at points below
the ring. We take the positive direction to be upward. Then, the force acting on an
electron on the axis is
F
eqz
=−
+
4
0
π
c
h
/
.
For small amplitude oscillations
z
R
<<
and
z
can be neglected in the denominator. Thus,
F
eqz
R
4
0
3
π
.
The force is a restoring force: it pulls the electron toward the equilibrium point
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This note was uploaded on 01/25/2011 for the course PHYSICS 17029 taught by Professor Rebello,nobels during the Fall '10 term at Kansas State University.
 Fall '10
 Rebello,NobelS
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