Review
 Please fill in the charges on your entrance
ticket…place + or – signs where they belong
Remember…+ charge does not mean
protons…we don’t touch the nucleus
Electricity only involves electrons or a lack of electrons
- charge
+ charge
http://www.youtube.com/watch?v=Gy9JRQAffbo
# 1 Conservation of Charge
 In a neutral atom, there
 Protons, electrons
are as many _____ as
_______, so there is no
(net) charge on the atom
If an electron is removed
from an atom, the atom
is no longer _______
(positive, negative, neutral)
 Neutral
What does Conservation
mean?
THE PRESERVATION OF
EXISTING CONDITIONS
Conservation of Charge
 An atom with more
 Positively
positive charges
(protons)than negative
are said to be ____
charged.
 A charged atom is called
a(n )_____.
(ion, force, repulsion, attraction)
 ion
What are the other 2 Law of Conservation we
have mentioned in class?
 1) Law of
Conservation of
Energy…energy is
neither created nor
destroyed, it simply
changes forms
 2) Law of
Conservation of
Momentum..momentum
does not change unless
an external force acts
upon it
Conservation of Charge
 The total amount of Electric Charge in a system does
not change…. when particles are destroyed, equal
numbers of positive and negative charges are destroyed.
 First proposed by Benjamin Franklin
 Most evidence indicates that the net charge in the universe
is zero
#2 Free Electrons
 Electrons in the (outer, inner) rings or shells of atoms are
bound more loosely to the nucleus
 Such electrons tend to break free from the nucleus and
wander around amongst other nearby atoms
 Such electrons are called free electrons
The youngest children in a family are similar to free
electrons…held less tightly by the parents
 http://www.youtube.com/watch?v=ZMhHzucl9lI
Free electrons
Such movement of these free electrons creates an
electric current

 Materials with large numbers of free electrons are
called electrical conductors. They conduct electrical
current.
# 3 Conductors
 Movement of the electrons physically from one place
to another is slow.
 Transfer of the energy from one electron to another
happens fast.
 Metals are good conductors
#3 Insulators
 Insulators have tightly
bound electrons
 Which make them poor
conductors of electricity
 Examples- rubber, glass,
ceramic, wood,
styrofoam, air
Main Idea
 Whether a substance is classified as a conductor or
an insulator depends on how t______ the atoms of a
substance hold their e______.
 Tightly, electrons
#4 Semiconductors
 Some materials are good insulators (as good as
glass) in their solid form, but become good
conductors (as good as Copper) if even one atom in
ten million is replaced with an “impurity” called
doping
 They can be made to behave as insulators and
sometimes as conductors
 AKA- transistors, LEDs, solar cells
 They are the foundation of modern electronics
Semiconductors
 Silicon and Germanium crystals are the most common
semiconducting materials formicroelectronics.
 Anything that's computerized or uses radio
waves depends on semiconductors.
 Clockwise from top: A chip, an LED and a transistor are all made from
semiconductor material. See more electronics parts pictures.
Silicon Valley
 1/3 of the companies relocated to Austin, Texas from
Silicon Valley
#5 Superconductors
 Discovered in 1911, by a Dutch physicist, at
temperatures near absolute zero, certain metals
acquire almost infinite conductivity (zero resistance).
Once an electric current is established in a
superconductor, the electrons flow indefinitely and a
magnetic field is created
 Uses: Superconducting magnets are some of the
most powerful electromagnets known…used in MRI