Download Chapter 6 * Electricity

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How do charges interact and build up?
Electric force: the force between
charged objects.
 Electric field: a region around a charged
object where the electric force is
exerted on other objects.
 Static Electricity: the buildup of charges.
 Conservation of charge: charges are
neither created now destroyed.
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Friction: when two objects rub against each
other.
Conduction: when two objects have direct
contact.
Induction: when an object becomes
charged without touching a charged
object.
Polarization: when all of the charges
particles go to one side of the object.
Static discharge: the loss of static electricity
and return to a neutral state.
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Protons are positive, electrons are
negative – when they come close to one
another, they are attracted to each
other.
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Particles with similar charges repel each
other.
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Electric fields and forces get weaker with
greater distance.
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In an electric field, the field lines always
point away from positive charges and
toward negative charges.
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Most objects have no charge, but can
become charged by losing or gaining an
electron.
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If an object loses electrons, it becomes
positive; if it gains electrons, it becomes
negative.
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Charging by friction: transfer of electrons
from one uncharged object to another
by rubbing them together.
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Charging by conduction: transfer of
electrons from one object to another by
direct contact.
› Electrons transfer from the object with a
negative charge to the object with a
positive charge.
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Charging by induction: transfer of
electrons without touching; if a metal
comes near a negative object, the
electrons will repel and the protons will
all move toward the end of the metal
object closest to the charged object.
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Charging by polarization: individual
atoms in an object have charged ends
that are attracted to charged objects.
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Charged particles eventually lose/gain
electrons from the air to balance out.
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Static discharge often produces a spark,
especially during the winter because
objects hold on to charges better in dry
air.
Lightning formation:
 Water droplets in clouds become
charged.
 Electrons move to areas of positive
charge (clouds become polarized).
 This causes the ground to also become
polarized.
 The electrons at the bottom of the cloud
are attracted to the protons at the
surface, and a large spark is formed.
How is Electric Current made?
 How do conductors differ from
insulators?
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Electric current: the continuous flow of
electric charges through a material.
Electric circuits: a complete, unbroken path
that charges can flow through.
Conductors: a material through which
charge can flow easily.
Insulators: materials that do not allow
charges to flow.
Semiconductors: materials that sometimes
act like conductors and other times like
insulators.
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Electric current is measured in amperes,
of amps (A).
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The number of amps is the amount of
charge flowing past a given point each
second.
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If an electric circuit is broken, the charge
stops flowing through the material.
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Conductors – most metals
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Insulators – rubber, plastic, glass, wood,
etc.
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The atoms in conductors have loosely
bound electrons that move more freely
than insulators.
How affects current flow?
 What is Ohm’s Law?
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Voltage: the difference in electric
potential energy per charge between
two points in a circuit.
 Resistance: the measure of how difficult
it is for charges to flow through an
object.
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Potential energy from a battery gets
turned into different energy forms.
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Voltage energy causes charges to keep
flowing through a material.
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The greater resistance, the less current
there is per voltage.
Resistance is measured in ohms.
 If more than one path is available, an
object will flow through the path with
least resistance.
 Current flows better in:
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› Wide wires
› Short wires
› Conductors
› Lower temps
What is a circuit made of?
 What is Ohm’s Law (review)?
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Ohm’s Law: resistance in a circuit is equal
to voltage divided by the current.
 Series circuit: a circuit that only has one
path.
 Parallel circuit: a circuit that has more
than one path.
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Circuits have the following parts:
 Energy source, such as a battery.
 Resistors (transform electrical energy into
other forms)
 Conducting wires to carry the current
 A switch to turn the circuit on and off
Series Circuit:
 Has one path
 If one light goes out, all of the lights go
out.
 Current decreases as more lights are
added, so the lights get dimmer.
Parallel Circuit:
 Has more than one path.
 If one light goes out, the others remain lit.
 The brightness of the bulbs stays the
same regardless of how many lights are
attached.
How can you calculate electric power?
 What are some safety precautions with
electricity?
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Power: the rate at which energy is
converted from one form to another.
Short circuit: a connection that allows
current to take the path of least resistance.
Third prong: part of most electrical plugs.
Grounded: when an electrical circuit is
connected to the ground.
Fuse: device that melts when it is too hot.
Circuit breaker: device that turns off when it
is too hot.
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Power is measured in Watts (or kilowatts)
and can be found by multiplying the
voltage by the current.
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Lights that use up energy more quickly
(brighter lights) have a higher power.
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The total amount of energy used is equal to
the power of the appliance multiplied by
the amount of time the appliance is used.
› Energy = power x time
A frayed wire is an example of a short
circuit; there is a path with lower resistance
than the actual circuit.
 Third prongs that are grounded help absorb
any extra shock, protecting buildings and
people.
 Fuses melt when they become too hot,
causing the circuit to become
disconnected.
 Circuit breakers bend away from circuits
when they become too hot, also
disconnecting the circuit.
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