2. Electrostatics: Electrical charges at rest
Law of Electrostatics: Like charges repel,
Unlike charges attract
Conductors: Free electrons allow
conduction of charge
+
+ +
++
+
metal
+
+ +
++
+
e-
3. Insulators (non-Conductors): Tightly
bound electrons do not conduct
charge readily
+
+ +
++
+
wood
Semi-Conductors: Silicon and Carbon,
among others that fall in between good
conductor and good insulators. Often used
in computer chips and other electronics.
No electron
transfer!
4. Electroscope: Device used for detecting
charges:
+
+ +
-
--
Coloumb’s Law: Electric Charge (Q) exerts a
force that depends directly on the charges
and inversely on the distance between the
charges!
5. Charge is determined by the surplus or
deficiency of electrons in relation to protons
and is measured in coloumbs (C)
1 C = 6.25 X 1018
electrons
This is a lot of charge-- most charges are
measured in microcoloumbs (µC)
1 µC = 10-6
C
Coloumb’s Law:
F =
kQ1Q2
r2
k = 9 X 109
N•m 2
/C2
this value is for charges separated by
air
Demo’s
6. An electrostatic charge of 60.0 µC exerts a
force of 175 N on a charge of 50.0 µC. How
far apart are the charges?
Q1 = 60.0 µC
Q2 = 50.0 µC
F = 175 N
r = ?
r =
kQ1Q2
F
= (9 x 109
N•m 2
/C2
)(60.0 x 10-6
C)(50.0 x 10-6
C)
175 N
= .391 m
7. Electric Field and Electric Field Intensity
Gravitational Field
Lines of Force q
q
q
q
Electric Field
m
8. Electric Field Lines of Force:
Electric Field Intensity (E): Force that acts on
a small test charge (+) in the field
E =
F
q
Units: N/C
