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#Post#: 15--------------------------------------------------
Physics - Circuit Connections
By: Dietrech Date: October 21, 2013, 9:35 am
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[font=comic sans ms]Two Types of Connections
When there are two or more electrical devices present in a
circuit with an energy source, there are a couple of basic means
by which to connect them. They can be connected in series or
connected in parallel. Suppose that there are three light bulbs
connected together in the same circuit. If connected in series,
then they are connected in such a way that an individual charge
would pass through each one of the light bulbs in consecutive
fashion. When in series, charge passes through every light bulb.
If connected in parallel, a single charge passing through the
external circuit would only pass through one of the light bulbs.
The light bulbs are placed within a separate branch line, and a
charge traversing the external circuit will pass through only
one of the branches during its path back to the low potential
terminal. The means by which the resistors are connected will
have a major affect upon the overall resistance of the circuit,
the total current in the circuit, and the current in each
resistor. In Lesson 4, we will explore the affect of the type of
connection upon the overall current and resistance of the
circuit.
A common physics lab activity involves constructing both types
of circuits with bulbs connected in series and bulbs connected
in parallel. A comparison and contrast is made between the two
circuits.
The main questions of concern in a lab activity such as this are
typically the following:
As the number of resistors (light bulbs) increases, what
happens to the overall current within the circuit?
As the number of resistors (light bulbs) increases, what
happens to the overall resistance within the circuit?
If one of the resistors is turned off (i.e., a light bulb
goes out), what happens to the other resistors (light bulbs) in
the circuit? Do they remain on (i.e., lit)?
In conducting the lab activity, distinctly different
observations are made for the two types of circuits. A series
circuit can be constructed by connecting light bulbs in such a
manner that there is a single pathway for charge flow; the bulbs
are added to the same line with no branching point. As more and
more light bulbs are added, the brightness of each bulb
gradually decreases. This observation is an indicator that the
current within the circuit is decreasing.
So for series circuits, as more resistors are added the overall
current within the circuit decreases. This decrease in current
is consistent with the conclusion that the overall resistance
increases.
A final observation that is unique to series circuits is the
affect of removing a bulb from a socket. If one of three bulbs
in a series circuit is unscrewed from its socket, then it is
observed that the other bulbs immediately go out. In order for
the devices in a series circuit to work, each device must work.
If one goes out, they all go out. Suppose that all the
appliances in a household kitchen were all connected in series.
In order for the refrigerator to work in that kitchen, the
toaster oven, dishwasher, garbage disposal and overhead light
would all have to be on. In order for one device in series to
work, they all must work. If current is cut from any one of
them, it is cut from all of them. Quite obviously, the
appliances in the kitchen are not connected in series.
Using the same collection of wires, D-cells and bulbs, parallel
circuits can be explored in the same manner. The affect of the
number of resistors upon the overall current and the overall
resistance can be investigated. The diagrams below depict the
usual means of constructing the circuit with parallel
connections of light bulbs. One will note that a study of the
overall current for parallel connections requires the addition
of an indicator bulb. The indicator bulb is placed outside of
the branches and allows one to observe the affect of additional
resistors upon the overall current. The bulbs that are placed in
the parallel branches only provide an indicator of the current
through that particular branch. So if investigating the affect
of the number of resistors upon the overall current and
resistance, one must make careful observations of the indicator
bulb, not the bulbs that are placed in the branches. The diagram
below depicts the typical observations.
It is clear from observing the indicator bulbs in the above
diagrams that the addition of more resistors causes the
indicator bulb to get brighter. For parallel circuits, as the
number of resistors increases, the overall current also
increases. This increase in current is consistent with a
decrease in overall resistance. Adding more resistors in a
separate branch has the unexpected result of decreasing the
overall resistance!
If an individual bulb in a parallel branch is unscrewed from its
socket, then there is still current in the overall circuit and
current in the other branches. Removing the third bulb from its
socket has the affect of transforming the circuit from a
three-bulb parallel circuit to a two-bulb parallel circuit. If
the appliances in a household kitchen were connected in
parallel, then the refrigerator could function without having to
have the dishwasher, toaster, garbage disposal and overhead
lights on. One appliance can work without the other appliances
having to be on. Since each appliance is in its own separate
branch, turning that appliance off merely cuts off the flow of
charge to that branch. There will still be charge flowing
through the other branches to the other appliances. Quite
obviously, the appliances in a home are wired with parallel
connections.
The affect of adding resistors is quite different if added in
parallel compared to adding them in series. Adding more
resistors in series means that there is more overall resistance;
yet adding more resistors in parallel means that there is less
overall resistance. The fact that one can add more resistors in
parallel and produce less resistance is quite bothersome to
many. An analogy may help to clarify the reason behind this
initially bothersome truth.
The flow of charge through the wires of a circuit can be
compared to the flow of cars along a tollway system in a very
crowded metropolitan area. The main sources of resistance on a
tollway system are the tollbooths. Stopping cars and forcing
them to pay a toll at a tollbooth not only slows the cars down,
but in a highly trafficked area, will also cause a bottleneck
with a backup for miles. The rate at which cars flow past a
point on that tollway system is reduced significantly by the
presence of a tollbooth. Clearly, tollbooths are the main
resistor to car flow.
Now suppose that in an effort to increase the flow rate the
Tollway Authority decides to add two more tollbooths at a
particular toll station where the bottleneck is troublesome to
travelers. They consider two possible means of connecting their
tollbooths - in series versus in parallel. If adding the
tollbooths (i.e., resistors) in series, they would add them in a
manner that every car flowing along the highway would have to
stop at each tollbooth in consecutive fashion. With only one
pathway through the tollbooths, each car would have to stop and
pay a toll at each booth. Instead of paying 60 cents one time at
one booth, they would now have to pay 20 cents three times at
each of the three tollbooths. Quite obviously, adding tollbooths
in series would have the overall affect of increasing the total
amount of resistance and decreasing the overall car flow rate
(i.e., current).
The other means of adding the two additional tollbooths at this
particular toll station would be to add the tollbooths in
parallel fashion. Each tollbooth could be placed in a separate
branch. Cars flowing along the tollway would stop at only one of
the three booths. There would be three possible pathways for
cars to flow through the toll station and each car would chose
only one of the pathways. Quite obviously, adding tollbooths in
parallel would have the overall affect of decreasing the total
amount of resistance and increasing the overall car flow rate
(i.e., current) along the tollway. Just as is the case for
adding more electrical resistors in parallel, adding more
tollbooths in parallel branches creates less overall resistance.
By allowing for more pathways (i.e., branches) by which charge
and cars can flow through the bottleneck areas, the flow rate
can be increased.[/font]
#Post#: 34--------------------------------------------------
Re: Physics - Circuit Connections
By: Isofunfix Date: March 2, 2015, 6:21 am
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#Post#: 39--------------------------------------------------
Re: Physics - Circuit Connections
By: Dammaberlin Date: April 27, 2015, 7:39 am
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#Post#: 46--------------------------------------------------
Re: Physics - Circuit Connections
By: smileonion Date: May 11, 2015, 11:30 pm
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#Post#: 49--------------------------------------------------
Re: Physics - Circuit Connections
By: Karenza Date: May 25, 2015, 4:24 am
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#Post#: 58--------------------------------------------------
Re: Physics - Circuit Connections
By: Actcher Date: June 22, 2015, 11:50 pm
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#Post#: 129--------------------------------------------------
Re: Physics - Circuit Connections
By: Coconut Date: January 16, 2019, 11:14 pm
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#Post#: 149--------------------------------------------------
Re: Physics - Circuit Connections
By: Dealfisx Date: October 17, 2019, 4:08 am
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