Transcript Electrostatics

ELECTROSTATICS
Electric Force
Whiteboard Particle Model
(remember sticky tape lab?)
How you can make a balloon
stick on the wall?
What is occurring on the atomic level
that lets you do this?
The atom
• The atom has positive charge in the nucleus, located in
the protons. The positive charge cannot move from the
atom unless there is a nuclear reaction.
• The atom has negative charge in the electron cloud on
the outside of the atom. Electrons can move from atom
to atom without all that much difficulty.
• You charge the balloon by rubbing it on hair or on a
sweater, and the balloon becomes negative. How can it
stick on a neutral wall?
Whiteboard Particle Model
(remember sticky tape lab?)
How you can make a balloon stick on the wall?
1.
1.
What is occurring on the atomic level that lets you do this?
Wall
• Molecules in the wall become polarized.
• Electrons move away from the surface repelled
by the excess negative charge on the balloon.
• This creates a positive surface that the balloon
can stick to
++++-
Wall
What is making them repel?
•A force
Whiteboard Particle Model
What happens to the vanes of
the electroscope when you bring
a negatively charged object
near it?
What is occurring on the
atomic level that makes
the vanes do this?
Pole
Vanes
Electrons are repelled by the
negative charge and are
conducted into the vanes.
The vanes become negative
and repulsive.
What is making them repel?
•A force
If Object is Positive (no whiteboard)
What happens to the vanes?
Pole
Vanes
If Object is Positive (no whiteboard)
What is making them repel?
•A force
Coulomb’s Law
• Coulomb’s law tells us how the magnitude of the
force between two particles varies with their
charge and with the distance between them.
kq1q2
F 2
r
• k = 8.99  109 N m2 / C2
• q1, q2 are charges (C)
• r is distance between the charges (m)
• F is force (N)
What direction are the forces on C?
+
-
-
A
B
C
Net Force is in what direction?
To the left