The Effect of Length and Thinkness of a Wire on Its Resistance
I am trying to investigate that how the length and thickness of a wire
affects its resistance.
What is electric charge and current?
Back to the everyday objects again: objects are made of molecules,
molecules are made of atoms, and atoms are made of electric charges
Therefore when you look at an object, don't imagine that it is made of
little tiny atoms. Instead, imagine that it's made of something even
smaller: little tiny electric charges. Matter is made of vast
quantities of electric charge, but the positive charge exactly cancels
Atoms might be made of charges, but atoms are unbreakable, right?
Wrong. Atoms are easily broken up. It is the NUCLEUS of an atom which
is difficult to shatter. It's quite easy to shred atoms by pulling the
negative electrons away from the tiny positive nucleus in the center
of an atom. When we rubbed the balloon on our hair, we were pulling
atoms apart. We should not think of atoms as if they were unbreakable
little solid balls. Atoms are more like liquid droplets made of
electrical charge. When atoms come together to form everyday objects,
the charges which form the outside of the atoms get all mixed
together. It's as if the world was made of charged particles, half of
them being the negative electrons, and the other half being the
positive cores of atoms.
What would happen if we could make the electric charges flow around
inside of an object? Then we would have an electric current
. Now you
know what an electric current really is. It's that simple. An electric
current appears whenever the negative charges in an object are forced
to flow through the positive charges, or when positive charges are
forced to flow through negative ones.
Everyday objects are made of Electric Charge: objects are made of
molecules, molecules are made of atoms, and atoms are made of positive
and negative charges. Electric charge is a kind of material substance,
but it is not atoms, instead it is the stuff that is inside of the
atoms. If we could place equal quantities of positive charge and
negative charge together, what would be the result? Neutral matter.
What is A.C and D.C?
The type of electricity commonly used is alternating current or AC
electricity. As the name implies, the current alternates in direction
as opposed to the direct current (DC) electricity that you get from
batteries. The AC and DC generators are similar, but AC was proven to
be a more effective way to transmit electrical power. AC is the
electricity we have in our homes, and it powers our television, lights
DC electricity is a direct flow of electrons through a conductor such
as a metal wire. A battery or DC generator usually provides a source
of electrons and the potential or voltage between the positive (+) and
negative (-) terminals. This flow of electrons through a wire can be
thought of as similar to the constant flow of water through a hose.
Alternating Current or AC electricity is a back-and-forth movement of
electrons in a wire, similar to sloshing water back-and-forth in a
hose. When the force of a negative (-) charge is at one end of a wire
and a positive (+) potential is at the other end, the electrons in the
wire will move away from the (-) charge, just like in DC electricity.
But if the charges at the ends of the wires are suddenly switched, the
electrons will reverse their direction.
The major advantage that AC electricity has over DC is that AC
voltages can be transformed to higher or lower voltages. This means
that the high voltages used to send electricity over great distances
from the power station can be reduced to a safer voltage for use in
This is done by the use of a transformer. This device uses properties
of AC electromagnets to change the voltages.
If you make an electromagnetic by wrapping a wire around a iron rod
and use AC electricity, the magnetic field will alternate at the same
rate as the electric current changes. If another wire is wrapped
around the rod, the changing magnetic field will create an AC current
in that wire.
What is especially interesting about this phenomenon is that the
voltage created in the second wire depends not only on the voltage in
the first wire but also on the ratio of the number of turns around the
This type of AC electromagnet with two sets of wires is called a
The AC transformer is a way to easily change the voltage the
electricity, something that more difficult to do with DC electricity.
This invention gave AC a tremendous advantage over DC as a source of
our electricity, because of the ability to easily transform voltage up
In electronics we are dealing with voltage, current and resistance in
Voltage is the electrical force and is a measure of the potential
difference between two terminals of a battery or any component of a
system. The mains have a voltage of 240v whereas battery systems use a
much safer 12 or 24 volts. In the same way as height affects the flow
of water, voltage affects the flow of current in a circuit.
Temperature affects the voltage of a cell as the voltage goes down if
it is warmer. It is measured in VOLTS.
Current is the movement of electrical charge - the flow of electrons
other charged particles through the electronic circuit. The direction
of a current is opposite to electrons flow direction. Current is
measured in AMPERES (AMPS, A).
Resistance causes an opposition to the flow of electricity in a
circuit. It is used to control the amount of voltage and/or amperage
in a circuit. It is measured in OHMS.
A temperature sensitive resistor usually made from specially processed
oxides that are used to sense end of charge temperature rises and
terminates high rate charging.
An electrical component which restricts the amount of electricity
allowed passing through it.
The electrons move rapidly around the nucleus. When electrons move,
free of the nuclei of atoms, and there is a net flow, this flow is
called electricity, or an electric current. This might be compared to
a flock of sheep moving north together, while the shepherds do not.
Electric charge can be directly measured with an electrometer.
Electric current can be directly measured with a galvanometer. Static
electricity is not a flow of electrons at all. More correctly called a
"static charge", it refers to a body that has more or fewer electrons
than are required to balance the positive charge of the nuclei. When
there is an excess of electrons, the object is said to be "negatively
charged". When there are fewer electrons than protons, the object is
said to be "positively charged". When the number of electrons and the
number of protons are equal, the object is said to be electrically
"neutral". Say, if there is a longer or thicker wire, then the number
of electrons will increase, there the force of resistance will also
The movement of electrical charges in a conductor; carried by
electrons in an electronic conductor (electronic current) or by ions
in an ionic conductor (ionic current). The electrical current always
flows from the positive potential end of the conductor toward the
negative potential end, independent of the actual direction of motion
of the differently charged current carrier particles.
An Atom, each shell has a maximum amount of electrons it can hold, 1st
shell-2 electrons and 2nd shell - 8 electrons.
Ohm's Law says that there is a relationship between these three
factors. So if you know two of the values you can easily work out the
V = I x R
I = V / R
R = V / I
The "V over I and R triangle" should help you to remember these three
equations. If you know the current and resistance and want to
calculate the voltage, you use the first equation. If you know the
voltage and resistance and want to calculate the current, you use the
Lastly, if you know the voltage and current and want to calculate the
resistance, you use the third equation.
Normally open switch
Primary or secondary cell
Battery of cells
Light Emitting Diode
Light emitting diode
a.c. power supply
A.C. power supply
Light Dependent Resistor
Light dependent resistor
Relay switch (normally open)
From the above knowledge, I predict that as the length
of the wire
increases its resistance will increase. I also believe that as the
thickness increases, the resistance increases.
I believe this because as the length or thickness increases, so does
the number of electrons that move. So there will be more resistance
forcing against the electrons. There will be more resistance forcing
against the free electrons.
We repeated the test three times for the length of the wire and done
the thickness of the wire three times for each thickness.
§ Variable Resistor
§ Crocodile clips
§ Different length and thickness wires
§ Metre ruler
1. I had to collect all the apparatus named above and I had to set it
up as shown below.
2. Move the wire along each 10 cm and record the current and voltage
reading from the multimeters, keeping in mind the thickness of the
3. Repeat this test three times.
4. Measure the current and voltage on three different lengths on
different thickness. Keep the lengths constant.
5. Take the results down.
You should keep your hands dry because electricity conducts
electricity easily through water. You have to check for un-insulated
wires because they are a risk to your and others safety. Never play
with the apparatus as you will be playing with electricity and could
potentially get shocked. Never eat food or drink near the apparatus as
this may affect it. Always check that everything is correct before
turning on the power as a single mistake could be possibly fatal.
I will be using different variables in this experiment. My dependant
variables are: the battery, temperature, and the apparatus. My
independent variables are the length of wire and the thickness of the
wire. There are a wide range of length results but there are not many
I found out that as the length of wire got longer and the thickness
increased, the resistance went up. This is evidence for my prediction.
The graphs are sloped and are straight lines of best fits.
The current graph shows that the current has a slight slope. The
current decreases as the wire gets longer. There is one anolymous
result on my current graph and it is on the 0.25mm thickness, at 100cm
and I have circled the result. The general trend on the graph is that
the thicker and shorter the wire, the higher the current.
On my voltage graph all the points slope slightly upwards, they are
generally parallel to each other. The graph shows the as the wire gets
thicker and longer, the voltage increases.
On my resistance graph the points also have a slight slope. The points
slope upwards and are also generally parallel to each other. The
general trend is, as the wire gets thicker and longer, the resistance
increases. The lines of best fit are commonly straight. My scientific
knowledge backs up my prediction by saying there are more electrons
when the wire is longer and thicker. My results prove my hypothesis
I feel I planned the experiment quite well; all the apparatus were set
up as advised. The circuit was a confusing at the beginning of the
experiment so I could not record results from the start of the
experiment. However, once I started doing the results, I realised that
they were easy. The test worked better than I had hoped because I
thought I would only acquire a minute number of outcomes. I believe
that my prediction was very good based on my scientific knowledge and
my results table. I repeated my results three times; I did this to
attain the average results table. Using this table I plotted my
graphs. There were a wide range of results which helped plot the
graphs. There were problems with the results though. The first problem
is that resistance creates heat, and increased heat in a conductor
also increases the resistance. This will therefore exaggerate results
as the wire gets longer, because a longer wire has more resistance, so
it will create more heat, and therefore more resistance, and therefore
more heat, and so on. This is made worse by the heat conductive nature
of metals due to their free electrons.
The theory behind this is that when a substance increases in
temperature, its atoms vibrate more. This means that the free
electrons are more likely to hit a vibrating particle.
If I were to repeat the experiment, it would be much easier and I
might even be able to obtain more results to make my work even more
accurate. I had one anolymous result, as I stated above. The cause of
this result may have been to the fault of the temperature. The
resistance graph should have been a straight line but they were
slightly curved and they did not go through the origin. Temperature is
a factor which affects the wire and this has also affected my results.
If I were to do the test again I would keep in mind the room
temperature so my results would become even more reliable.