Static Electricity
• History of charged
particles – 1900’s
• Electrons(-) in shells
• Protons(+) in nucleus
• Neutrons(0) in nucleus
Static Electricity
• The SI unit for electric charge is the
coulomb: C
• Electrons carry the smallest possible
negative charge. The charge on one
electron -e is 1.60x10-19C
• Protons carry the smallest possible
negative charge. The charge on one
proton +e is 1.60x10-19C
Static Electricity
• An object may be charged by rubbing it
by another object. Only electrons may
be lost or gained by a rubbed object.
• If the atom loses electrons,
it will become____
• If the atom gains electrons,
it will become ____
Static Electricity
Protons are never transferred!!!
Charges are never created nor
destroyed. =
Law of Conservation of Charge
Rubbing to lose/gain e–Rub a glass rod with silk
– the silk gains -e and the glass loses -e
–Rub a rubber rod with fur
– the fur loses -e and the rod gains -e
–They will be oppositely charged and
therefore attract each other.
Table 19-1
Triboelectric Charging
Material
Rabbit fur
Glass
Human hair
Nylon
Silk
Relative charging with rubbing
++++++
+++++
++++
+++
++
Paper
+
Cotton
-
Wood
--
Amber
---
Rubber
----
PVC
-----
Teflon
------
Charging by Contact
• Conductors – electrons are easily
transferred
• (ex: metals – Ag, Au, Cu)
• Insulators – electrons do not move easily
from one location to another – (ex: wood,
plastic, air)
Figure 19-5
Electrical Polarization
Charging by Contact
Conduction
• If two objects
touch, they will
have the same
charge and REPEL
(unless they were neutral)
• Like charges REPEL
• Demo- Rub
balloon in your
hair!
• The Law of Electrostatics
• LIKES REPEL
• OPPOSITES ATTRACT
Demos
• 1. Paper & Golf Tube
• 2. Golf Tube & 2” x 4” x 8’
• 3. Balloon on the Wall
Conduction is just like sharing
• To charge an object by touching it
with another charged object. The
second object shares the charge and
is always the same charge as the first
object.
• Examples of sharing
Charging by Conduction
IC
-10
0
A) Both 0
B) Both –10
C) Both –5
D) Both +5
-10
0
-5
-5
IC
+10
0
IC
In which direction do the electrons move
A) Left B) Right C) Neither D) Both
+10
+5
0
+5
IC
-10
-14
-10
-14
-12
-12
IC
+10
+14
IC
Which sphere is more negative and in which
direction do the electrons flow?
A) right, right
B) right, left
C) left, right
D) left, left
+10
+12
+14
+12
IC
+10
-14
IC Final Charge after sharing is
A)–24
B) –12
C) –2
D) +2
+10
-14
-2
-2
Sharing when objects are not the same size.
-10
0
Sharing ?
-
-
-
0
-
-10
-
-
-
-
Grounding
• Sharing charge between an
extremely large object, like the
EARTH, and a small object is called
grounding. All the charge winds up
in the earth and no charge is on the
small object.
Induction
• Charging by induction
–Case #1 - bring a negative object near
–Case #2 - bring a positive object near
Charging by Induction
Charging by Induction
Charging by Induction
Charging by Induction
Charging by Induction
Charging by Induction
t = 5 sec
Balloons on the Ceiling
• Why do
balloons stick
to the ceiling
when rubbed
on your hair?
Balloon on the Ceiling or Wall
Using a Van de Graaff Generator
Van de Graaff in action
Wild Hair
Demos with the VDG
•
•
•
•
1.
2.
3.
4.
A hair raising experience
Packing pellets
Ribbon
Silver ball
Lightning
• Where is the
safest place in a
lightning storm?
Find the BOLT?