Summary of chapter 22
Prepared by Dr. A. Mekki
There are two
types of electric charges in nature;
Positive charge (proton) and negative
charge (electron).
An object is negatively
charged if it has gained electrons.
Insulators are
materials in which electric charge (electrons) are not free to move. Materials
such as glass, rubber, and plastic are insulators.
Semi-conductors have
electrical properties between metals and insulators.
N m2/C2
eo is the permitivity of free
space and k is the electrostatic constant, q1
and q2 are the charges of
the two particles and r is the
distance between the two charges.
If the two charges have same
signs, there is repulsion
between them.
+
+
or
- -
If the two charges have opposite
signs, there is attraction between them.
1 2
r
-F
F
+
4. The
shell theorem
(i)
A charge q is outside a uniformly charged shell carrying a charge Q.
The
force on the charge q in both cases is
If the charge q in inside the uniformly charged shell then the force on
the charge q is ZERO.
The elementary charge is that of the electron e =
1.6 x 10-19 C.
Any charge on a body is an integer multiple of the electron charge,i.e.,
Q = n e, n = 1, 2,
Electric charge is always conserved. It can be
transferred from one body to another but cannot be lost.