Coulomb’s Law (1)
Electrostatic force between two charged particles:
r
+
F =
1 |q1 q2 |
|q1 q2 |
=
k
4πǫ0 r2
r2
Permittivity constant: ǫ0 = 8.854 × 10−12 C2 N−1 m−2
Coulomb constant: k = 8.99 × 109 Nm2 C−2
+
q1
F 21
+
F12
+
q2
~21 = −F
~12 .
Action-reaction pair of forces: F
Newton′ s law of gravitation
Gravitational force between two massive particles:
F =G
m1 m2
r2
Gravitational constant: G = 6.673 × 10−11 Nm2 kg−2
7/1/2008
[tsl4 – 1/2]
Coulomb’s Law (2)
Coulomb’s law for electrostatic force in vector form:
~12 = k q1 q2 r̂12 ,
F
2
r12
.
r2 − ~
r1 ,
~
r12 = ~
r12
. ~
.
r̂12 =
r12
Electric force in hydrogen atom:
Average distance: r = 5.3 × 10−11 m.
Elementary charge: e = 1.60 × 10−19 C.
|q1 q2 |
r2
(8.99 × 109 Nm2 /C2 )(1.60 × 10−19 C)2
=
(5.3 × 10−11 m)2
= 8.2 × 10−8 N.
F =k
7/1/2008
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