# • Objects can be charged by rubbing dissimilar materials.

```• Objects can be charged by rubbing dissimilar materials.
• There are two kinds of charge leading to both attractive and repulsive
forces unlike the gravitational force.
• The quantitative form of the force between charged objects was found by
Coulomb using a torsion balance.
• The quantitative form is called Coulomb’s law:
(vector form)
12
12
12
where q1 and q2 are point charges.
• Inverse square law just like gravity but usually much large in magnitude in
situations encountered in our daily lives (except earth).
• The force on charge q1 due to a collection of point charges is given by:
 


F1  F12  F13  F14 ...
• The force on charge q1 due to a continuous volume of charge:


F1   dF
Electrostatic force due to line of charge
1
Electrostatic force due to ring of charge
Electrostatic force due to disk of charge
2
Binomial theorem
n
n
n
n
(1  x) n    x 0    x1    x 2    x 3  ...
0
1
2
3
Spherical coordinates
3
```