Electricity and Magnetism Notes – Week of March 21, 2016

```Electricity and Magnetism
Notes – Week of March 21, 2016
Review:
 All matter (solids, liquids, gases, plasmas) are made of atoms.
 Atoms are made of smaller particles:
o Protons- positive charge (+)
o Neutrons- no charge (+/-)
o Electrons- negative charge (-)
 Atoms have the same number of protons and electrons
Electricity:
 Positive and Negative Charges
o Atoms are electrically neutron- no charge overall
o Atoms can become negatively charged if they gain an electron.
o Atoms can become positively charged if they gain a proton.
o A positively (+) or negatively (-) charged atom is called an ion.
 Electrons Move in Solids
o Electrons can move from one atom to another OR can move from object to object.
 One way to move is through rubbing (friction).
 Static charge- imbalanced electric charge on an object
How does an object become electrically charged? ___________________________________________
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Ions Move in Solutions:
 Table salt (sodium chloride) is made of sodium ions and chloride ions that cannot move through
solids. When dissolved in water (liquid) the ions break apart and are free to move.
Water molecules break up the
sodium chloride bond.
Electric Forces:
Electricity and Magnetism
Notes – Week of March 21, 2016

attractive (+/-) or repulsive (+/+ OR -/-) force exerted by all charged objects on each other
o Example: rubbing wool on a balloon will increase the charge on one of the objects

get stronger as two charges get closer; get weaker as two charges get farther away from one
another
How does the electric force between two charged objects depend on the distance between them?
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Electric Field:
Electricity and Magnetism
Notes – Week of March 21, 2016
o
o
Positive Charge
surrounds every electric charge and exerts forces on other electric charges
gets stronger as charges get closer; gets weaker as charges get farther away from one
another
Negative Charge
Like Charges
Insulators and Conductors:
Electricity and Magnetism
Notes – Week of March 21, 2016


Insulator- a material in which electrons cannot move easily from place to place
o Examples: plastic, wood, glass, rubber
o protect from electric shock by blocking electrons from moving through the material
Conductor- materials that electrons can move through more easily
o Examples: metals (copper, gold, aluminum)
o allows electrons to move freely within insulation
Induced Charge: electric discharge (static electricity- shock with a door knob, lightning)
 charges are pulled from one object to another rapidly
“As you walk across the floor, you rub
electrons from the carpet onto the
electrons then spread out over your
“As you bring your hand close to the
metal doorknob, electrons on the
doorknob move as far away from
your hand as possible. The part of the
doorknob closest to your hand is left
with a positive charge.”
“The attractive electric force
between the electrons on your hand
and the induced positive charge on
the doorknob might be strong
enough to pull electrons from your
hand to the doorknob. You might
see this as a spark and feel a mild
electric shock.”
Georgia Science: Grade 8, McGraw Hill Glencoe, New York, New York: page 589.

Grounding: a way to absorb excessive voltage from electric current
Electricity and Magnetism
Notes – Week of March 21, 2016
o
Examples: lightning rod on buildings, placing rubber on the “feet” of appliances
Electric Current: the flow of electric charge
 Flow of Electric Current:
o Solids: the flowing charges are electrons
o Liquids: the flowing charges are ions (positive or negative)
 Measured in Amperes (A)
Circuit: a closed conducting loop through which electric charges flow continuously
 Simple Circuit: contains a source of electrical energy and an electric conductor connected to the
source of energy
o Example: source- battery
o Example: electric conductor- wire




Voltage: a measure of how much electrical potential energy each electron can gain (V)
How a Current Flows:
o Electrons move slowly in an electric circuit
o When the ends of a wire are connected to a battery, the battery produces an electric
field in the wire.
o The electric field forces electrons to move toward the positive battery terminal.
o Electrons move and collide with other electric charges in the wire and then moved in
another direction.
o Continuous collisions moving the electrons toward the positive battery terminal.
 Electrons may undergo more than ten trillion collisions each second.
Batteries: supplies energy to an electric circuit
o When positive and negative terminals are connected to an electric circuit, the electric
potential energy of the electrons is increased.
o Chemical reactions create an electrical field in the circuit causing electrons to move
away from the negative terminal and toward the positive terminal.
Battery Life:
o don’t supply energy forever
o some are rechargeable
o when chemical reactions stop, the battery is “dead”
Resistance: the amount of difficulty electrons to flow through a material
Electricity and Magnetism
Notes – Week of March 21, 2016





measured in ohm (
)
can be converted into thermal energy and sometimes light
Buildings Use Copper Wires:
o Copper has low resistance
o Good conductor
o Low heat- doesn’t get hot enough to start fires
Resistance of Wires:
o short wires- less resistance
o long wires- more resistance
o narrower- more resistance
o thicker- less resistance
Lightbulb Filaments: made of wire so narrow it has high resistance
o becomes hot enough to create heat and light
Electric Circuits:
 Voltage and Resistance:
o increase in resistance = decrease in electric current
o decrease in resistance = increase in electric current
 Ohm’s Law: When the voltage in a circuit increases, the current increases. However, if the
voltage in the circuit doesn’t change, then the current in the circuit decreases when the
resistance is increased.
 Series and Parallel Circuits:
o Circuits: control the movement of electric current by providing paths for electrons to
follow
o SERIES CIRCUIT: a circuit that has only one path for the electric current to follow.
 If the path is broken, the current will no longer flow.
o
PARALLEL CIRCUIT: a circuit that has more than one path for the electric current to
follow.
Electricity and Magnetism
Notes – Week of March 21, 2016

If one path is broken, electrons continue to flow through other paths.
How many different paths can electric current follow in a series circuit? ________________________
How many different paths can electric current follow in a parallel circuit? _______________________
types of
electric
charge
opposite
charges
like
charges
current in a circuit
depends on
exerts force that
causes charges
to move
current
in a
circuit
depends
on
Electricity and Magnetism
Notes – Week of March 21, 2016
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