Investigate the factors That Affect the Flow of Electricity Through a Conductor.
GCSE Physics Coursework
Centre Number: 12736
Nower Hill High School
P ;O ; A ;E ;SP&G
Scenario: Investigate the things that affect the flow of electricity
through a conductor.
Plan
Aim:
In order for an electric circuit to work charge must flow throughout the
circuit. This flow of electricity or charge is known as the current, and in
my experiment I aim to investigate how the flow of current through a
conductor is varied when altering variables.
Background information:
As I have explained the current is the flow of charge and is measured in
amps, this tells us how much charge is flowing through any point in the
circuit in one second. As charge is measured in coulombs, one ampere is when
one coulomb of charge passes in one second. This charge flow, therefore an
electric current flowing trough metal conductors is caused because of the
flow of electrons. In an atom the electrons are arranged in shells. The
electrons in the shells closest to the nucleus are held strongly. The
further the shell is from the nucleus the weaker the electrons are held.
Thus, the outermost shell holds the electrons held weakest.
Metals only contain one or two electrons in the outermost shell of each
atom, therefore these are lost easily. As these electrons are held so weakly
to the nucleus, they can easily break free from the atom when a push is
supplied by the voltage of the battery, they are therefore ¡°free¡±
electrons. Voltage is a measure of the amount of electromotive force, e.m.f
(energy) needed to push each coulomb of charge. Therefore voltage is a
measure of joules per coulomb. As the atoms have lost negatively charged
electrons when they have been pushed, they now become positive ions due to
the unbalanced charge. The atoms or ions (when electrons are lost) in metals
are arranged in regular crystal patterns. The free electrons from each atom
can move through this crystal structure. Due to the metal being connected
to a power supply, the electrons flow in one direction towards the positive
terminal- thus there is an electric current, a flow of charge (electrons).
As the electrons are flowing, the energy produced is kinetic. This kinetic
energy is obtained by energy being transferred from the e.m.f. (Push)
supplied by the power source.
I have explained that charge flows because it is pushed around a circuit by
the e.m.f provided by the power source. The greater the e.m.f, the greater
the current, as this means that more charge is flowing through the each
point in the circuit in one second, because a greater push is supplied, so
more energy is transferred. However there is also another factor to consider
that affects the current, the resistance. Resistance is a measure the
electrical property of a material that determines how much it opposes the
current, causing it to decrease. For conduction to occur the resistance must
be small enough to allow current to flow.
Different metals have different resistances due to their different molecular
structures. If there are a smaller number of free electrons, or if they are
less more mobile because their outermost shell is closer to the nucleus,
there will be a smaller number of electrons (smaller charge) flowing through
any point of the circuit in one second because it is harder for them to
flow. Therefore there is more resistance, causing a smaller current.
Resistance is caused by collisions occurring between the moving electrons
(flowing due to current) and the positive ions. This results in the
electrons slowing down and losing kinetic energy, because the energy is
transferred to the ions. Consequently, the resistance of as substance causes
the current to decrease, as the charge flows slower, because there is a
decrease in kinetic energy, as collisions constantly make them slow down.
Therefore the greater the resistance the smaller the current.
As I have explained current is affected by the voltage and the resistance of
an electrical circuit. The greater the voltage the greater the current; the
greater the resistance. Ohm¡¯s law explains the direct connection between
this:
V=IR
I=V/R
R=V/I
Ohm¡¯s law only applies to ohmic conductors such as metals. It also states
that the current through a metallic conductor is proportional to the voltage
when the temperature is kept constant:
I ¡Þ V
This is because the current increase according to the push supplied by the
voltage. The voltage/current is constant?
Variables:
There are a number of variables I can alter in this experiment that will
theoretically alter the flow of current through a conductor. However, I am
only going to concentrate on one variable, as this will allow me take make a
more detailed conclusion. I am now going to decide upon which variable I
should change for my experiment by briefly examining each one.
A possible variable I could alter to change the amount of current flowing
through a conductor is the voltage. An increase ...
This is a preview of the whole essay
Variables:
There are a number of variables I can alter in this experiment that will
theoretically alter the flow of current through a conductor. However, I am
only going to concentrate on one variable, as this will allow me take make a
more detailed conclusion. I am now going to decide upon which variable I
should change for my experiment by briefly examining each one.
A possible variable I could alter to change the amount of current flowing
through a conductor is the voltage. An increase in the voltage would cause
an increase in the current because there is a greater push supplied by a
greater e.m.f. Meaning more energy is more energy is transferred to the
electrons. Therefore they have a greater current as they have a greater
amount of kinetic energy. However, I am not going to use this variable
because there is less scope to it. This is because a number of scientific
theories such as ohms law have already been developed for this variable.
A variable I could choose is changing the conductor itself. This would alter
the current that flow through the conductor itself because the amount of
resistance created by a conductor depends on the number of electrons in the
outer shell, and how far the shell is from the nucleus of the atom. By
altering the resistance in this manner the current would consequently be
varied. Nevertheless, I have decided not to use this variable as a change in
the electrical properties of a substance cannot be easily measured,
therefore it would be difficult to conclude from an experiment such as this.
Another variable to consider is altering the temperature. By increasing the
temperature, the resistance of the wire would also increase, therefore
decreasing the current flow through a conductor. This happens because as the
metal wire of the circuit, or the conductor heat up the positive ions
oscillate faster. They therefore cause electrons to lose more energy when
they collide with the ions, meaning the electrons flow more slowly, causing
the resistance to increase and the current to decrease. However, as I cannot
control the temperature, due to limited resources, I cannot experiment with
this variable.
Changing the cross-sectional area of the conductor can also be used the
variable for my experiment. When increasing cross-sectional area of a
conductor the current flow through it will increase because the resistance
decreases. This is because when increasing the cross-sectional area the
electrons are given an additional path to flow through. Therefore, there are
fewer collisions with ions, meaning the current will be increased as the
resistance is decreased. Altering the diameter of a conductor works in a
similar way. However I have decided not use this variable in my experiment
as the range of my results would be limited because it would difficult to
alter the cross-sectional area, or the diameter of the conductor to large
degree.
For my experiment I have chosen to investigate how the length of the
conductor alters the current passing through that conductor. I have chosen
to experiment with this variable because I have the resources to investigate
it effectively and I think there will be a large scope for this
investigation. In my prediction I will discuss what I think will happen when
altering this variable.
Pilot Study
I have conducted a pilot study to familiarise myself experiment, make
modifications to it, and determine certain values to use for the experiment.
As I am finding how the current flow is affected through a conductor, I am
going to be measuring the current using an ammeter. I found when conducting
this test trial that when the voltage was to high the components overheated,
but when it was to low the ammeter would not give an accurate current
reading ¨C I needed to find values to create a balance between these to
factors so that the components did not overheat and the current could still
be measured.
Firstly I decided to use constantan wire as my conductor for this
experiment. This is because by using a wire as the conductor, length can be
measured easily and the diameter is kept constant. I chose constantan wire
in particular because it was available to me and it had has a fairly high
resistance, so it will not overheat or melt easily.
The pilot study helped me to determine what voltage I should use I my
experiment. I needed to find a voltage range which was high enough so that a
measurable current (using an ammeter) was able flow the circuit, but low it
enough so that the safety was ensured and so the components would not be
damaged by overheating. I found that the range a voltage of 6 volts best
suited this.
However, I did not need to find a certain diameter of wire to fit the
requirements because this did not greatly affect the current flow or was the
cause of overheating
I also had to find over what range to take my measurements, and a rate at
which to increase the variable by. i.e. what range of the length of wire to
use and how much to increase the length by each time. I found that the range
between 5-50 cm was most suitable as it was large enough to obtain accurate,
reliable results on which to base a conclusion, and was not too time
consuming. I also decided to increase the length of wire at a rate of 5cm at
a time as this allowed a good variation in the current.
Other factors, in particular the variables I have already discussed will
affect my results. In order to make the test fair I am going to keep the
following variables constant so that my results are as accurate as possible.
I have already stated that I will keep the type of wire (constantan) the
same and although I have not decided on a particular diameter for the wire,
it will be kept constant in order to ensure that the experiment I am
conducting is fair.
In addition I found that when altering different lengths of the wire
(constantan, used as conductor), the potential difference (voltage) across
the length of wire also changed. As I am measuring the relationship between
the current and the length, in order to keep my test I had to keep this
value constant. I did so by altering the voltage on the power pack, so that
the potential difference across the wire was always kept constant, at 6v.
A factor that will affect my results if not kept constant is the room
temperature. As I have already explained this will affect the current of
across the conductor, but due to limited resources I am unable to control
this.
In order to make my results more reliable and accurate, I am going to take
three measurements for each result so that I am able to take an average.
Additionally my measurements will be made more precise as I am using
suitable and accurate instruments, such as the voltmeter and ammeter,
accurate to 2 decimal places. To further increase the accuracy of my results
I will use the apparatus precisely and properly by taking measurements
carefully. I will use the apparatus appropriately by using techniques such
as ensuring that the positive terminal of the ammeter and voltmeter is are
always connected so that they are closer to the positive terminal of the
power pack. I will use my equipment accurately by using techniques such as
ensuring the ruler is always parallel to the wire when measuring its length
and recording the voltage and current only when the voltmeter and ammeter
display stable readings. I also had to check for zero-errors in my equipment
such as making sure the power pack, voltmeter and ammeter were operating
correctly.
Also safety will be a major issue when conducting my experiment. I will take
the necessary precautions such as conducting myself in an appropriate
manner, choosing a voltage that is safe and suitable and turning off
equipment when it starts to overheat.
Doing my pilot I came up with the following experiment:
Apparatus:
Power pack, constantan wire (approximately 55cm in length), voltmeter,
(copper) circuitry wires, ammeter, crocodile clips and ruler
Method:
) Take necessary safety precautions.
2) Check for zero errors in the equipment.
3) Gather apparatus: Power pack, constantan wire, voltmeter, circuitry
wires, ammeter, two crocodile clips and a ruler.
4) Set up circuit as shown in diagram, attaching both crocodile clips at
either end) of the constantan wire. Set the voltage of the power pack to six
volts
5) Using the ruler measure a 5cm distance of the wire and connect the
crocodile clips at this distance.
6) Activate the power pack and record the voltage, using the voltmeter, and
the current using the ammeter after the values have sustained to a constant
level.
7) Repeat steps 4-5 for lengths of wire increasing 5cm at a time, until you
have recorded the result for 50cm.
8) Repeat each result 3 times, so that from this an average can be
sustained.
9) Repeat any anomalous results.
Diagram
Prediction:
I predict that as the length of the wire increases the current flowing
through the constantan wire (conductor) will decrease. This is because when
increasing the length of the wire there is a greater mass of the substance.
Therefore there are a greater number of positive ions. Resistance is caused
by electrons colliding with the positive ions, causing the electrons to slow
as their kinetic energy has been transferred to the positive ions (this
would show as a decrease in current). When increasing the number of positive
ions, by increasing the length of the wire, more collisions will occur
between them and the electrons. Due to more collisions, the electrons will
flow more slowly as they have lost more kinetic energy. Therefore the
current will decrease as the length of the wire increases.
I also predict the current will be inversely proportional to the length of
the wire:
L ¡Þ 1/C
This is because resistance is caused by electrons colliding with ions. If
the number of positive ions is doubled, by doubling the length there will be
twice as many collisions, hence twice as much resistance (as resistance
occurs due to the occurrence of this). Hence I think resistance will be
proportional to the length. On a graph this would appear as a straight line
in a positive correlation.
L ¡Þ R
When the resistance is doubled, due to the length of the wire being doubled
the current will be halved as twice as many collisions mean the electrons
will be moving half as fast, as they have lost twice as much kinetic energy.
This means that current and resistance are inversely proportional, and
because length and resistance are proportional, current and length will also
be inversely proportional.
Obtaining
As I have explained in my pilot study I carried out many procedures to
ensure safety and make my results as accurate and precise possible. Despite
this some results were anomalous (crossed out in table), therefore in order
to make the test more fair, and the average more precise, I had to re-do
these results. In the table below are the results obtained from my
experiment. In order to make the results more precise I carried out results
and found the average to 2 decimal places.
Table showing how the length of the constantan wire affected the Current
flowing through it:
Length of Wire (cm) Current (amps)
2 3 Average
5 1.55 1.61 1.59 1.58
0 1.26 1.53 1.23 1.28 1.26
5 1.00 1.02 1.06 1.03
20 0.88 0.85 0.89 0.87
25 0.77 0.74 0.74 0.75
30 0.71 0.65 0.66 0.67
35 0.55 0.60 0.87 0.63 0.59
40 0.53 0.52 0.70 0.56 0.54
45 0.50 0.49 0.48 0.49
50 0.42 0.45 0.47 0.45
In my prediction I also commented on how the resistance of the wire would be
affected by the length. In order to provide evidence for this I have also
calculated the resistance for each piece of wire using ohm¡¯s law from the
voltage and current. Therefore I have included the voltage and current in my
table to display where I obtained the resistance from.
Table showing how the length of the constantan wire affects the resistance.
Length Of Wire (Cm) Voltage (Volts) Average Current (amps) Resistance (Ohms)
5 6.00 1.58 3.80
0 6.00 1.26 4.76
5 6.00 1.03 5.83
20 6.00 0.87 6.90
25 6.00 0.75 8.00
30 6.00 0.67 8.96
35 6.00 0.59 10.17
40 6.00 0.54 11.11
45 6.00 0.49 12.24
50 6.00 0.45 13.33
Analysis
On the two previous pages I have drawn up graphs to display my findings.
First I am going to discuss the resistance graph so that I can then comment
on the current.
The straight line, of a positive correlation shows that as the length of the
conductor (wire) increases, the resistance of the wire increases, meaning
that they are proportional. This because when the length is increased the
number of positive ions are increased to that degree. As resistance is
caused by electrons colliding with positive ions, when there are more
positive ions, there are more collisions to that degree. Hence when length
is increased to a degree so is the resistance, meaning they are
proportional. This proves the part of my prediction, when I stated that this
would be the case:
L ‡ R
The second graph is of an inversely proportional curve showing that the
current is inversely proportional to the length of the wire. In my
prediction I also stated that this would be the case. This is because when
increasing the length of the wire the resistance increases to that degree.
This means that there will be that many times more collisions, causing the
current to decrease inversely to that degree.
C ‡ L
Unlike in my prediction, I have now concluded that this happens for another
reason. The current is inversely proportional to the length because
electrons are accelerating. This happens because in order for there to be an
electric current, the electrons (flow of charge) must be continuously
speeding up. If this was not the case the flow of the electrons would
gradually decrease and then stop because their kinetic energy is being lost
when colliding with ions. This does not happen as the current reading on an
ammeter does not gradually decrease or eventually show there is no current.
Therefore the electrons must be accelerating. As a current reading is
stable, it shows the average flow of electrons. When electrons collide they
only lose some of their kinetic energy but all of it. The electrons then
accelerate again but because energy has been lost in the previous collision,
they de not re- gain the same speed. With each additional collision, the
energy lost (unable to be re-gained) accumulates, causing a smaller average
flow of electrons meaning the current is lower. When the length of the wire
increases, there are more collisions between electrons and ions, meaning the
average flow of electrons is smaller. Hence the current decreases as the
length of the wire increases. As the electrons move slower with more
collisions (due to a longer wire), they lose less energy as the collisions
are gradually becoming smaller. Therefore the rate at which the electrons
are losing energy is gradually decreasing. This explains the decreasing
(inversely proportional) curve, of the graph.
Evaluation
Overall my experiment went well as I was able to obtain results on which I
could base a conclusion. The results were fairly accurate as most of them
fit the line of best fit on the graph. Despite this, the results cannot be
considered very reliable due to a number of limitations caused by flaws in
my method.
A major limitation I have already discussed is that if the room temperature
increased or decreased it would have affected my results, as this would have
altered the resistance and therefore the current flowing through the
conductor. However as I have not recorded the change in room temperature I
am unable to say to what extent they affected my results.
Another factor affecting the results is when the electrons transferred their
energy to the ions; the ions vibrated causing the wires to heat up. This
would have increased the resistance of the conductor. This would have made
the test unfair, as the following results would have been affected by the
heating affect of the previous ones. This would have affected my results to
a large degree.
Another factor to take into account is human error. Although I undertook
procedures to keep this minimal this would have still been evident, such as
in my measuring in the length of the wire. However, this would only affect
my results slightly, because the affects of this are minimal.
These factors, particularly the heating of the wires, are the likely cause
of anomalous results.
To improve these limitations in my method, I could improve it primarily be
conducting the experiment in controlled temperature conditions. There is no
practical method reducing the heating affect of collisions, but it could be
prevented by waiting a few minutes until the equipment has cooled down and
then continuing with experiment. This would produce more fair results, but
it would be too time consuming. The best way to reduce human error is by
using more advanced equipment, in order to measure the length of the wire.
Another limitation in my conclusion is that it cannot be taken generally as
I have only conducted the experiment using one type of conductor and one
type of voltage- my aim was to see how the length affected the current
flowing through a conductor in general. In order t make the conclusion more
general, and provide further evidence for it I could do further experiments
such as using different voltages and conductors.
Bibliography:
Book Title Author Publisher
Key Science- Physics Jim Breithaupt Stanley Thornes Ltd
Physics For You Keith Johnson Stanley Thornes Ltd.
