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Chapter 34 Electric current
Concepts that students must know:
Potential Difference –causes flow of __________—the
flow continues until both ends of the conductor reach a
common potential.
Electric current is the flow of __________.
Electric current is measure in ______________ [unit].
1 ampere = 1 coulomb of charge/1 ________
1 Coulomb = __________ x 10 18 electrons
Voltage sources— dry cells, wet cells, ____________,
supply examples of each
All charges need a potential ____________ to flow.
Alternators/generators convert mechanical energy to
__________ energy.
Dry and wet cells (batteries) convert _____________
energy to electrical energy.
Outlet voltage = 120 volts means __________ joules of
energy/ 1 coulomb of charge.
Electrical resistance— resistance to flow of ____________.
Thick wire has _________resistance than thin wire.
Longer Wires have ___________ resistance.
Increased temperature = increased resistance.
Resistance is measured in _________.
Ohms Law—current is directly proportional to
___________ and inversely proportional to resistance.
Current = voltage/ resistance
1 amp = 1 ______/1 ohm
Average bulb = 100 ohms
Toaster = 20 ohms (low resistance permits high current to
create high ________).
Ohms Law and electric shock—damaging effects of shock
are the result of ___________ passing through the body.
Wet body has 100 ohms of ____________ (allows for
high current)
Dry body has 500,000 ohms of resistance (less likely
to allow for high ______________)
Ground wire (third wire) is for ____________
(provides path of less resistance)
DC and AC current—DC is single ________ and AC
alternates direction 60/sec.
AC current is the primary type of current used to transfer
___________ from one place to another. _________current
is the primary type of current used as storage.
Converting AC to DC.
Diodes are devices that are “one way” valves that
allow __________ flow in _____ direction only. A
capacitor stores the filtered half cycle (time delay) to
smooth out the pulse output.
Electric fields travel through circuits at nearly the speed of
light, but electron do ________.
The speed of electron flow—DC electricity travel at approx
_________________ meter in 3 hours.
AC electricity reverses direction ____________ times /sec
and therefore electrons stay at the _________ place.
The source of electrons in a circuit—Electrons already in
the ______________.
Electrons ______________.
Energy comes from the outlet—(Power Company is an
_______________ company)
120 volts = 120 joules/1 coulomb (6 x 1018 __________)
Energy, not electrons, comes from wall _________.
Electric Power—rate at which electric energy is converted
into another form of ________ is power.
1 watt = 1 ampere x 1 ________.
60 watts = .5 amps x _______volts
1 kilowatt = ________ watts
1 kilowatt hour = 1000 kilowatts x 1 ________
Chapter 35
Electric circuits—circuit cannot have any gaps
(__________)
Series circuit—__________ path way for electrons to flow
between terminals of battery.
Parallel circuit—has branches, each of which is a separate
path for the flow of _________.
Important characteristics of Series circuits—
1. Electric _________ has a single pathway through the
circuit.
2. The current is resisted by the ______ of the resistance
of all devices along the circuit.
3. The current is numerically the voltage of the source
divided by the __________ resistance of the circuit
(Ohms law).
4. Ohms law applies separately to each device—the
voltage drops across ________ device depends
directly on its (each device) resistance.
5. The sum of the individual voltage drops is
__________ to the voltage of the source.
The main disadvantage of a series circuit is that if one
device fails _________ of the devices in the circuit will
work.
Homes are wire in parallel so that a device can be
___________ without affecting the operation of any other
devices.
Parallel circuits—electrical devices connected to the same
__________ points of an electric circuit.
Important characteristics of Parallel circuits—
1. Each device connects the same two points and the
___________ is therefore the same across each device.
2. The total __________ divides among the parallel
branches. Current passes more readily into devices of
low resistance, so the current in each branch is
___________ proportional to the resistance of the
branch. Ohms law applies separately to each branch.
3. The total current in the circuit is equal to the
_________ of the currents in parallel branches.
4. As the number of parallel branches is increased, the
overall resistance of the circuit is ____________. This
means the overall resistance is less that any one
(resistance) of the branches.
Schematic diagrams;
Symbols are used to represent certain circuit elements.
Discuss battery symbols
1. Resistor symbol __________
2. Wire ___________
3. Open switch ______________
4. Closed switch ________________
Combining resistors in a compound circuit
Parallel circuits and overloading-- Because adding more
branches in a ___________ circuit decreases total
resistance, more current is used. Lines that carry an unsafe
amount of current are said to be ____________ which may
melt insulation and cause a fire.
Fuses –devices connected in ________ to protect a circuit
from overload. Fuse ribbon melts and must be replaced.
Circuit breakers—device connected in __________ to
protect from overload. Device uses magnets and bimetallic
strips to open the switch when it senses too much
_________. The breaker must be turned off and then back
on after the overload condition is_________________.