Chapter 34 Electric current and 35 Electric circuits
Standards 5
a, b
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 amps
1 ampere = 1 coulomb of charge/1 second
1 Coulomb = 6.25 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 120 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 volt/1 ohm
Average bulb = 100 ohms
Toaster = 20 ohms (low resistance permits high current to create high heat).
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 current)
Ground wire (third wire) is for ____________ (provides path of less resistance)
DC and AC current—DC is single direction 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. [Demonstrate on board].
Electric fields travel through circuits at nearly the speed of light, but electron do
________.
The speed of electron flow—DC electricity travel at approx 1 meter in 3 hours.
AC electricity reverses direction 60 times /sec and therefore electrons stay at the
_________ place.
The source of electrons in a circuit—Electrons already in the conductor.
Electrons vibrate
Energy comes from the outlet—(Power Company
energy company)
120 volts = 120 joules/1 coulomb (6 x 1018 electrons)
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 volt
60 watts = .5 amps x _______volts
1 kilowatt = ________ watts
1 kilowatt hour = 1000 kilowatts x 1 ________
.
Chapter 35
Battery and bulb
Discuss construction of bulb.
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
Use concept Dev Practice 35 to demonstrate this process
Use work sheets to practice.
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 repaired.