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ELECTRICITY
MR. ROCKENSIES
REGENTS PHYSICS
ATOMIC STRUCTURE
WHAT IS THE STRUCTURE OF AN
ATOM?
Li atom
3 protons
3 electrons
4 neutrons
ATOM
Na - e
ION
Na+
Cl + e
Cl-
N + 3e
N-3
WHAT ARE THE THREE SUBATOMIC
PARTICLES?
Particle
Proton
Neutron
Electron
Symbol
1
p
1
or
1
0n
0
-1e
1
1H
Charge
Mass
1 positive
elementary
charge =
+1.6 x 10-19 C
1 amu =
1.67 x 10-27 kg
(on the
reference table)
0
1 amu =
1.67 x 10-27 kg
1 negative
elementary
charge =
-1.6 x 10-19 C
1/1836 amu =
9.11 x 10-31 kg
1 e = 1.6 x 10-19 C (Coulombs)
6.25 x 1018 e = 1 C
On the
reference
table
Examples:
1)+10 e (elementary charges) formed by
An
atom losing 10 electrons
_______________________________
2) -4 e formed by
An
atom gaining 4 electrons
_______________________________
Examples:
1) What is the charge on 2 protons in
elementary charges? Coulombs?
2) What is the charge on 4 electrons in
elementary charges? Coulombs?
3) An object has a charge of -2C
a) Does the object contain more
protons or electrons?
b) How many more electrons than
protons does it contain?
STATIC ELECTRICITY
WHAT IS STATIC ELECTRICITY
1)The study of the transfer of electrons
between objects and the electrostatic
force that the charges exert upon each
other
2)Rubbing or contact produces equal, but
opposite charges.
HOW DO CHARGES BEHAVE?
1) Opposites attract:
-
+
2) Like charges repel:
+
-
+
3) Any charge attracts a neutral object:
+ - +
- - +
+ -
+ +
- +
- +
+ +
+-
+-- + - +
+ + - +
+ - +
LAW OF CONSERVATION OF
CHARGE
WHAT IS THE LAW OF CONSERVATION
OF CHARGE?
1. Charge is not created or destroyed. It can
be moved from one object to another, but
the total amount is constant (Like
momentum and energy)
2. Charge occurs in specific quantities,
integer multiples of the elementary charge
Ex: q=ne
where e = 1.6x10-19C and n=0, 1, -1, 2, 2, 3, -3…
PRACTICE PROBLEMS
+3
+5
If these two spheres come in to contact with each
other and then are separated, what will the resulting
charge be on each?
PRACTICE PROBLEMS
-2
+4
If these two spheres come in to contact with each
other and then are separated, what will the resulting
charge be on each?
PRACTICE PROBLEMS
If these three spheres come into contact
with each other and then are separated,
what will the charge on each be?
ELECTRIC FORCES
HOW EASILY DO ELECTRONS FLOW
THROUGH MATERIALS?
Electron motion depends on how tightly the
substance holds the electrons.
All materials fall somewhere along the spectrum
Conductors
(weakly bound
electrons) EX:
Metals - “sea of
electrons”
Ionic solutions
Charge will
move easily
through a
conductor.
Charge will
stay in place
on an insulator.
Insulators (tightly
bound electrons)
Organics – (rubber,
plastic, paper)
Crystalline Solids
(silicon, etc.)
WHAT ARE ELECTRIC FORCES?
Also called “Coulomb Forces”
Like charges repel
Opposite charges attract
Either charge will attract a neutral
HOW DO THESE FORCES INTERACT
WITHIN AN OBJECT?
On a conductor, all charge rapidly moves
to the outside surface due to repelling
forces.
Charge will always move to a lesser charges
or uncharged object, or “ground” (literally
earth)
- This is the reason we experience a
static shock
WHAT IS COULOMB’S LAW?
r
Fe = kq1q2
r2
Force between
two small
charges.
q1
q2
k = 8.99x109 N· m2/C2
(use 9.0x109)
k = the electrostatic constant
PROPERTIES OF COULOMB’S LAW
Positive forces indicate repulsion
Negative forces indicate attraction
Coulomb’s Law is an inverse-square law.
Fe
Ex: Doubling the distance
yields one-fourth the
force
r
PRACTICE PROBLEM
Force is a vector – multiple charges create
multiple forces. Find the resultant
+q1
+q2
Force from q2
-q3
Force from q1