Transcript section_1_and_2x

1.4 The motor generator
Sandia national lab - fusion device that makes electrons arc across the room
Where does Electricity come from?
Electricity is a form of energy produced by the movement of electrons from atom to
atom.
Electrons tend to stay put in their orbits (or "shells") as long as the atom has the same number of positively
charged protons and negatively charged electrons. When something upsets this balance, electrons leave their
orbits and become "free electrons."
Electricity =
Electrons
All matter is made up of very small particles called atoms. Atoms are made of even smaller particles called protons, neutrons, and
electrons
Part of
the Atom
proton
mass
1 amu
Charge
Location
+1
nucleus
Neutron
1 amu
0
nucleus
electron
0 amu
-1
electron
cloud
What is the Law of Electric Charges ?
Law of Electric Charges
Charged objects exert a force- a push or pull- on other charged objects.
The law states that like charges repel each other and opposite charges attract
each other
What is Electric Force?
What does electric force depend on?
Page 5
Electric force
The force between charged objects
The size of the electric force depends on two things.
The first thing is the amount of charge on each object. The greater the charge is, the greater t
electric force is.
The other thing that determines the size of the electric force is the distance between the
charges. The closer together the charges are, the greater the electric force is.
What is an electric field?
Electric
field
the region around a charged object in which an electric force
is exerted on another charged
object. A charged object in the electric field of another charged object is attracted or repelled
by the electric force acting on it.
Why are you NOT getting a shock by every object around you if
protons and electrons are charged objects?
Charge
Atoms have equal numbers of protons and electrons.
Because an atom’s positive and negative charges cancel each other out, atoms do not have a
charge.
An object becomes positively charged when it loses electrons.
An object becomes negatively charged when it gains electrons.
Friction
two objects rub against one another. One object absorbs electrons
from the other making both objects charged and attracted to each other.
Conduction
Electrons move from one object to another by direct contact
Induction
when charges in an uncharged metal object are rearranged without direct
contact with a charged object.
Give a brief summary of the three types of electrical transfer .
What is the Law of Conservation of Charges?
`
Conservation of charge
When you charge something by any method, no charges are created or destroyed.
The numbers of electrons and protons stay the same.
Electrons simply move from one atom to another, which makes areas that have different
charges.
Because charges are not created or destroyed, charge is said to be conserved.
http://www.youtube.com/watch?v=MTKXXbbiqRs&feature=related
What are the energy conversions here?
What's the best way for electricity to move from one place to another?
Electrical conductor
a material in which charges can move easily.
Most metals are good conductors because some of their electrons are free to move
copper
How do you prevent the electrical conductor wires in your house from
conducting electricity into the house starting a fire?
Electrical Insulator
A material in which charges cannot easily move.
Insulators do not conduct electricity because their electrons do not flow freely.
Plastic is one of the best insulators. All cords and wires in your house are wrapped
on plastic.
plastic coating
These jumper cables are made of
metal, which carries electric charges,
and plastic, which keeps the charges away from your hands.
Explain Static Electricity. ( page 8 )
Static electricity
the electric charge at rest on an object.
Static means not moving. The charges build up on an object and stay there until an opposite charge gets within the charges
field.
http://www.youtube.com/watch?v=uVVJZhUXZaY&feature=related
What is an electric discharge?
Electric Discharge
Charges that build up as static electricity on an object eventually leave the object. The loss of
static electricity as charges move off an object
What are the dangers of Lightning?
how do we protect houses and buildings from lightning?
Lightning Rods
http://www.youtube.com/watch?v=jiKNisWj-Hs
Section 2
An electric current is the rate at which charges pass a given point.
The higher the current is, the greater the number of charges that pass the point
each second.
Electric current is expressed in units called Amperes (AM PIRZ), which is often
shortened to amps.
Andre Ampere - French 1775-1836
The symbol for ampere is A.
And in equations, the symbol for current i
the letter I.
What are the two types of electric current?
There are two kinds of electric current—direct current (DC) and alternating current (AC).
In direct current, the charges always flow in the same direction.
In alternating current, the charges continually shift from flowing in one direction to flowing in
the reverse direction.
The average home has AC current that changes direction 120 times/second , or 60 cycles per second
Luigi Galvani - Italian
Voltage is the potential difference between two points in a circuit.
It is expressed in volts (V).
Voltage and Energy
Voltage is a measure of how much work is needed to move a charge between two points.
You can think of voltage as the amount of energy released as a charge moves between two points in the
path of a current.
The higher the voltage is, the more energy is released per charge.
Voltage of electricity always flows from where there is a lot of
electricity to where there is less electricity.
An electric eel can create a voltage of more than 600 V!
Electric Ray @ 45 V
Resistance
the opposition to the flow of electric charge.
Resistance is expressed in Ohms (Ω, the Greek letter omega).
In equations, the symbol for resistance is the letter R.
You can think of resistance as “electrical friction.”
The higher the resistance of a material is, the lower the current in the material is.
So, if the voltage doesn’t change, as resistance goes up, current goes down. An
object’s resistance depends on the object’s material, thickness, length, and
temperature.
Resistance and Material
Good conductors, such as copper, have low resistance.
Poor conductors, such as iron, have higher resistance.
The resistance of insulators is so high that electric charges cannot flow in them.
Materials with low resistance, such as copper, are used to make wires.
But materials with high resistance are also helpful.
For example, the high resistance of the filament in a light bulb causes the light bulb to
heat up and give off light.