Transcript series circuit - Madison County Schools

Bellringer
Restate Ohm’s Law as 3 different
mathematical equations.
Resistance = Voltage/Current OR
Ohms = Volts/Amps
Voltage = Current X Resistance
OR Volts = Amps X Ohms
Current = Voltage/Resistance OR
Amps = Volts/Ohms
Electric Circuits
part II
Series Circuits
• A series circuit has all the parts of the
circuit connected on one path.
• An example of a series circuit is a
circuit with a battery and two light bulbs
connected by a single wire.
Series Circuits
• Suppose a series circuit has two light
bulbs. If one burns out, the second bulb
goes out because the circuit is broken
when the first bulb burns out.
Series Circuits
• If you add resistors to a series circuit,
the resistance of the circuit increases.
• This can be shown as:
•R =R +R +R ...
Total
1
2
3
•Remember, Resistance is measured in
Ohms and uses the symbol Ω.
Series Circuits
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•
In a series circuit, the current throughout the
circuit is constant.
This can be shown as:
ITotal = I1 = I2 = I3...
Where current is represented by the letter I in
the equation, but is measured using the units
amperes or amps, and uses the units A.
Series Circuits
• Also, in a series circuit, as bulbs are
added in line, all of the bulbs become
dimmer.
• Each bulb adds more resistance to the
circuit, therefore, for a constant voltage,
when resistance increases, current
decreases.
Series Circuits
• An ammeter is an instrument used to
measure current.
Parallel Circuits
• A parallel circuit has more than one
path for current to take. There are
separate branches in a parallel circuit.
Each resistor may be on its own
branch.
Parallel Circuits
• Suppose a parallel circuit has two light
bulbs, each on its own branch. If one
light bulb burns out, the other light bulb
will stay lit. The second bulb stays lit
because it is on its own branch.
Parallel Circuits
• Because the voltage source (battery)
provides constant voltage, the only
factors that can change in a circuit are
resistance and current.
Parallel Circuits
• In a parallel circuit, when more
branches are added, the overall
resistance decreases, meaning that the
current will increase.
• Think blowing through one straw versus
blowing through 2 straws. Two straws
allow twice as much air through, but
your lungs are only capable of blowing
so much at a time.
•
Parallel Circuits
The major disadvantage of a parallel circuit is
that as you add more things in parallel, the
current draw on the source goes up with each
new branch. If the source cannot supply the
current that is demanded by the multiple
resistors of the circuit, the voltage will (must!)
decrease. This could be bad, as some
devices, notably motors, do not like to run at
low voltage and can actually be damaged if
voltage decreases too much.
Parallel Circuits
•A voltmeter is a device used to
measure voltage, or electrical potential
energy difference.
Parallel Circuits
• The circuits in your home are parallel.
• Electrical energy enters your home
through heavy-duty, low resistance
wires, and then branch out in parallel to
your wall sockets, then to appliances
and lights in each room.
• The voltage in most household circuits
is 120 V.