Cory Redding- MISEP
Part I: Model of Circuits (through section 3)
The first concept that was essential for developing my group’s model for circuits
was the idea that the arrangement of the equipment had to be closed and “circular.” We
made several observations in experiment 1.1 where, by trial and error, we observed under
what circumstances a light bulb would light and not light. My group noted the
arrangements in which the bulb lit up and termed those a closed circuit and conversely
named the arrangements when the bulb did not light up an open circuit.
To solidify our
idea of open and closed circuits, we examined a flashlight (1.3) and confirmed that the
flashlight would only light when the circuit was closed and all parts were touching. In
experiment 1.5, we explored which parts of the bulb needed to be connected to the
battery. This led us to our second major concept of our model for electric circuits,
conductors and insulators.
In experiment 1.6, my group tested several different materials to see if a bulb
would light, and if so, how brightly that bulb would light. We found that some of the
materials, such as copper and aluminum, allowed the bulb to light while other materials,
such as plastic and glass, did not allow the bulb to light. We termed the materials that
allowed the bulb to light conductors and materials that did not allow the bulb to light
insulators. In experiment 1.8, we applied our new knowledge of conductors and
insulators when we examined a light bulb. We noted that a light bulb contains both. For
example, the glass parts of the bulb were insulators and the metal parts of the bulb
(including the screw threads, rivet and wire) were conductors.
In experiment 1.11A, we utilized a switch to once again examine the concepts of
open and closed switches. We observed that when the switch was open, the bulb did not
light and when the switch was closed, the bulb did indeed light. In experiment 1.11B, we
rearranged the circuit so that when the switch was open, the light bulb DID light and
when the switch was closed, the light bulb DID NOT light. This allowed us to create our
definition for a short circuit. At this point in time, we did not have a name for what was
traveling through the circuit and tended to call it “the flow.” We observed that when a
there is a path without a light bulb, as there was when the switch was closed in 1.11B, the
bulb will not light because the flow preferred to travel the path without the light bulb.
Opening the switch in this experiment turned the bulb on because there was no longer a
Cory Redding- MISEP
path for the flow to travel without going through the bulb. The final part of section one
entailed synthesizing our knowledge of circuits thus far in order to correctly depict them
using circuit diagrams. We practiced using the symbols in exercises 1.13 and 1.14.
Circuit diagrams show electrical connections and not necessarily the physical layout of
the circuit. Practicing these diagrams allowed us to further construct our model of
electric circuits by requiring us to think about each connection and tracing the path of the
flow through each part of the circuit, including each part of the bulb. Which bulbs would
light? Was there a short? Were the circuits electrically the same?
To construct the next part of our model, we focused on the unknown “flow”
through the battery. In experiment 2.1, we observed that the wire was warmer on the
parts connected to the battery and cooler in the parts that were farthest away from the
battery. Although we did not have direct evidence, it was also at this point that we made
several major assumptions including:
•
The flow is traveling in a continuous loop through the circuit
•
The brightness of the bulb indicates the amount of flow through the bulb
•
If two identical bulbs are equally bright, then the flow is equal through them both
•
If one bulb is brighter than another, then the flow through that bulb must be
greater through the brighter bulb
•
If one bulb is dimmer than another, than the flow through that bulb must be less
through the dimmer bulb
•
We will now name the term for flow current (although we still do not know what
is flowing through the circuit)
In experiment 2.4, we set up a two bulb circuit called a series circuit and observed
that bulbs connected in this way are noticeably dimmer than that of a single bulb. From
this experiment, we began to reason that the current through the battery can change.
Because the bulbs the series were equal to each other, we concluded that they must be
receiving the same amount of current. The current was not used up in the first bulb and
switching the bulbs did not matter- they always remained equally bright. From that
observation, we concluded that the current must flow back to the battery.
In experiment 2.6, we set up two separate pathways with a bulb in each path. This
type of circuit is called a parallel circuit. The brightness of each of these bulbs was equal
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to each other and the same brightness as a single bulb. We concluded that the same
amount of current must be traveling through each of the bulbs because the brightness was
the same. When one of the bulbs was removed, the other bulb stayed lit and remained at
the same brightness, therefore the pathways must be independent of each other. It did not
get brighter as it did when the bulbs were in series. The amount of current coming out of
the battery in this parallel circuit must be more than that of the series circuit because the
brightness of a one bulb circuit is the same brightness as a two bulb parallel circuit; the
series is dimmer. Because our model equates brightness with the amount of current, there
must be more current in the parallel circuit. When more bulbs were added in parallel, the
brightness of each bulb remained equal to each other and equal to that of the single bulb.
In a series circuit, there is less current when more bulbs are added because there was
more “resistance” on the same path. We observed this in experiment 3.1. The big idea
that our group added to our model was that current can change across the battery
depending on the circuit.
Experiment 3.1 also allowed our group to further explore the idea of resistance.
We observed that as the amount of resistance increased, the brightness of the bulbs
decreased indicating a decrease in current.
In exercise 3.2, we hypothesized that
because the indicator bulb became brighter, the amount of current must have increased
and therefore the resistance must have decreased. We tested this hypothesis in
experiment 3.3. My group observed that when bulb C was added, the brightness of bulb
A became brighter. By adding another bulb in parallel to bulb B, the total resistance of
the circuit decreased while the total current through the circuit increased. Bulb A was in
series to bulbs B and C, and because it was “before” those two bulbs, it receives all of the
current while B and C only receive half of the current through A.
There is more total
current out of the battery because adding bulb C decreases the total resistance. This
essentially gave the current additional pathways on which to travel. My group often
referred to this as “traffic patterns.” If there are two roads as opposed to one road, more
traffic is able to flow. Our model now included the following:
•
When a bulb is added in parallel, the resistance decreases and the total current
through the circuit increases
Cory Redding- MISEP
•
When a bulb is added in series, the total resistance increases and the current
decreases
Experiments 3.5 and 3.6 allowed us to continue to explore the current through parallel
and series circuits however; we modified our model by adding the following:
•
Parallel branches are independent of one another when they are in parallel with
the battery.
•
When there is not a clear path to the battery, then the parallel branches are
dependent of one another.
•
The current may not split equally between the branches and will split depending
upon resistance.
Part II: Rank the Brightness
Circuit #1 A>D=C>B=C
In circuit #1, the current does not split equally between the path that bulb A is on
and the path that bulbs B and C are on. Because bulbs B and C are in series to each other
and have more resistance, bulb A will be brighter than B and C. Bulb A is brighter
because it is receiving more current than B and C because it has less resistance along that
pathway. Because the current does not split equally, bulb A will receive more current
and will be brighter, but our model does not allow us to calculate at this point exactly
how much more current bulb A receives.
The current then joins back together prior to entering the pathways of bulbs D and
E. These bulbs are in parallel to each other receive equal current and are equal in
brightness to each other. Because bulbs D and E must split the current, they must be less
bright than bulb A, which is receiving more than half of the total current. Therefore, bulb
A is the brightest. Bulbs B and C must be the least bright because they are splitting less
than half of the total current.
Circuit #2 H>???I=J??F=G???
In circuit #2, the current does not split equally between the pathway that bulbs F
and G are on and the pathway that bulbs H, I and J are on. Because pathway H offers less
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resistance, more of the current will travel through this pathway. Bulb H will receive the
most current because all of more current on this pathway must travel through this bulb.
The current then splits equally between bulbs I and J. These bulbs are in parallel to each
other and are each receiving half of more current.
The pathway that bulbs F and G are on receives less current when the current
splits because it has more resistance and therefore less current. These bulbs are equal in
brightness to each other. All of the current that travels through bulb F also travels
through bulb G and therefore they each receive all of less current. At this time, our
model does not allow us to compare bulbs F and G to bulbs I and J. We cannot say
exactly how much current is traveling through each of the bulbs.