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Chapter 20
Electricity
Section 1
Electric charge and static electricity
Section 1 vocabulary
• Electric force
• Conduction
• Electric field
• Induction
• Static electricity
• Static discharge
• Conservation of
charge
• Friction
Electric charge
• Charges that are the
same repel each other.
• Charges that are different
attract each other.
Electric force
• Electric field
• A region around a charged object where the
object's electric force is exerted on other
charged objects
• Electric field around a single charge
• Electric field around multiple charges
Static electricity
• Charges build up on an
object, but they do not
flow continuously
Transferring charge
• Charging by Friction
• The transfer of electrons from one uncharged objected to another
by rubbing
• Charging by Conduction
• The transfer of electrons from a charged object to another object by
direct contact
• Charging by Induction
• Movement of electrons to one part of an object that is caused by the
electric field of a second object
• Detecting charge
Static discharge
• When a negatively
charged object and a
positively charged object
are brought together,
electrons transfer until
both objects have the
same charge.
Section 2
Electric current
Section 2 vocabulary
• Electric circuit
• Conductor
• Insulator
• Voltage
• Voltage source
• Resistance
Flow of electric charges
• What is electric current?
• The continuous flow of electric charges through a
material
• Current in a circuit
• To produce electric current, charges must flow
continuously from one place to another.
• An electric circuit is a complete, unbroken path
through which electric charges can flow.
Conductors and insulators
• Conductors
• A material through which
charge can flow easily
• Transfers electric charge well
• Insulators
• A material through which
changes can not flow easily
• Does not transfer electric
charge well
Voltage
• Charges need energy to flow
• Voltage
• Potential difference
• Causes a current in an
electric current
• Voltage sources
• A device that creates a
potential difference in an
electric circuit
Resistance
• Current depends on resistance
• Resistance is the measure of how difficult it
is for charges to flow through a material.
• The greater the resistance, the less current
there is for a given voltage.
• Factors that determine resistance
• Path of least resistance
Section 3
Batteries
Section 3 vocabulary
• Chemical energy
• Battery
• Chemical reaction
• Wet cell
• Electrochemical cell
• Dry cell
• Electrode
• Electrolyte
• Terminal
The first battery
• Luigi Galvani
• Alessandro Volta
• Volta built the first electric battery by layering
zinc, paper soaked in salt water, and silver.
Electrochemical cells
• A simple cell
• Electrochemical cell is a device that transforms chemical energy
into electrical energy.
• Electrodes are two different metals immersed in a substance
• Electrolyte is a substance that conducts electric current
• The part of an electrode above the surface of the electrolyte is a
terminal
• Chemical reactions occur between the electrolyte and the
electrodes in an electrochemical cell.
• These reactions cause one electrode to become negatively charged
and the other electrode to become positively charged.
Electrochemical cells
• Batteries
• A combination of two or more electrochemical cells in a
series
• Wet cells
• An electrochemical cell in which the electrolyte is a liquid
• Dry cells
• An electrochemical cell in which the electrolyte is a paste
Section 4
Electric circuits and power
Section 4 vocabulary
• Ohm's law
• Series circuit
• Ammeter
• Parallel circuit
• Voltmeter
• Power
Ohm's law
• Ohm's results
• Calculating with Ohm's
law
• The resistance is equal
to the voltage divided
by the current
Features of a circuit
• First, circuits have devices
that are run by electrical
energy.
• Second, a circuit has a
source of electrical
energy.
• Third, electric circuits are
connected by conducting
wires.
Series circuits
• One path
• Resistors in a series
circuit
• Measuring current
• An ammeter is a device
used to measure
current.
Parallel circuits
• Several paths
• Resistors in a parallel circuit
• Measuring voltage
• A voltmeter is a device
used to measure voltage,
or electrical potential
energy difference.
• Household circuits
Electric power
• Power ratings
• Calculating power
• You can calculate
power by multiplying
voltage by current.
Paying for electrical energy
• The total amount of
energy used by an
appliance is equal to the
power of the appliance
multiplied by the amount
of time the appliance is
used.
Section 5
Electrical safety
Section 5 vocabulary
• Short circuit
• Grounded
• Third prong
• Fuse
• Circuit breaker
Personal safety
• Short circuits
• A connection that allows current to take the path of least resistance
• Electric shocks
• Grounding
• One way to protect people from electric shock and other electrical
danger is to provide an alternate path for electric current
• A circuit is electrically grounded when charges are able to flow
directly from the circuit into earth in the event of a short circuit.
• The third prong, which is round, connects any metal pieces of the
appliance to the ground wire of the building.
Breaking a circuit
• In order to prevent circuits from
overheating, devices called
fuses and circuit breakers are
added to circuits.
• A fuse is a device that contains
a thin strip of metal that will melt
if there is too much current
through it.
• A circuit breaker is a reusable
safety switch that breaks the
circuit when the current gets too
high.