Find out how the thickness and length of an electrical conductor affect its resistance.

Iron                                                Ceramic

Aluminium                                        Rubber

Most metals can be used as electrical conductors but for practical and economic reasons some of the main metals used are copper, aluminium and gold, because conductors are usually made into wire it is important that the material is capable of being drawn out into fine strands without breaking (ductile).

The positive charge or force required to start the passing and accepting of a free electron creating electricity can be created in several different manners; chemical energy (battery), solar energy (power collected from the sun in solar batteries or collectors, friction force (generators). This force is called Voltage

 

What is resistance?

Resistance is an effect, which prohibits the free movement of electrons through a material. It is caused by the electromagnetic and chemical properties of the material the electrons are trying to flow through in general the more free electrons available in a material the lower the resistance

The relation ship between voltage, current and resistance in an electrical circuit is given by Ohms law which states:-

The current flowing through a metal conductor is directly proportional to the voltage (p.d.) across its ends provided the temperature and other physical conditions remain constant.

 Resistance is calculated by the equation R=V/I where R is resistance V is the potential difference (voltage) and I is the current (or Amperage).This means that is you were to increase the amperage then the resistance would decrease

What factors affect resistance?

There are different factors that affect the resistance in a wire:

1. Length

The longer the wire the more force (voltage) is required to move the free electrons, its resistance is increased

2. Thickness

The thicker the wire the more free electrons are available to flow because the cross sectional area is greater, its resistance is reduced

3. Temperature

If the temperature of a conductor increases it expands and allows easier movement of the electrons and its resistance is reduced

4. Material

Some materials are better conductors that others because they have more free electrons in their atomic structure this makes their resistance lower

Aim

I would like to find out how the thickness and length of an electrical conductor affect its resistance. This will help me to understand why the electricity in my home is conducted in carried in large copper cables but the fuse wire that protects the circuit is only very small but carries the same current.  I am going to investigate how the length of the wire affects its resistance. I will use 5 different lengths of wire to do this.

Preliminary work

I am going to look at 3 different materials. Nickel chrome, copper and constantin. They are all of the same length and thickness. Using for thickness standard wire gauge (SWG) and the same voltage was applied at their ends.

The standard wire gauge (SWG) is a measure of thickness of wire its number is based upon the number of wires that can be placed side by side in an inch, the lower the number, the thicker the wire is and the larger it’s cross sectional area.

Using ohms law to calculate the resistance I obtained the following results

R = V/I

Nickel chrome

                5/0.3 = 16.7 Ohms

Constantine

                5/1.0 = 5     Ohms

Copper

                5/0.5 = 10   Ohms

I decided to use nickel chrome for the experiment I was going to undertake. Nickel chrome as the highest resistance, as you can see from the above results

Apparatus

1. An ammeter

To measure the current flowing in the wire

2. Voltmeter and power supply unit

To deliver and measure a voltage applied to the wire

3. crocodile clips and wire

To connect the meters, power supply end wire to be tested

4. metre ruler

To measure the wire to be tested

Above --Diagram of Apparatus Used

Prediction

Using ohms law ,the results from my preliminary work and my understanding of the way that the more free electrons that are present in the cross sectional area of the conductor the lower its resistance, also the longer the length of the wire the more voltage (pressure) will be required to move the free electrons along its length. I predict that the resistance of the wire will increase with its length and decrease with its thickness.

Method

The apparatus was set up as follows the power supply was connected by lead which went to the ammeter, the lead then went on to a crocodile clip that was used to connect to the test wire, another lead then returned current  to the power supply unit from the test wire.

The wire that was to be tested was already prepared, it was stapled on a long wooden board,

A connection was made on to the end of the wire with one of the crocodile clips the ruler was then used to measure the length of wire to be tested and the other crocodile clip was attached at this position. The voltage was set at 5volts and the current flowing was measured using the ammeter this result was then recorded on my result table. The crocodile clip was then removed and the ruler was then used to measure the next position and the clip was reapplied and the current flowing was retested. This procedure was repeated for all of the different lengths of wire. When all the test where complete on the

36 swg wire the same test where repeated on the 30 swg and 26 swg wire and all the results record in my table of results

Fair test

All variables other than those tested were kept constant, voltage, temperature, thickness & material. Because the resistance of the test wire can be affected by heat and the procedure of passing the test current through the wire will result in a heating effect it was that the current flow changed the longer the duration of the test. I decided to take the initial current reading from the ammeter at each test before the heat had built up sufficiently to affect the result.

The resistance could also be affected by loose electrical connections between any of the equipment but the crocodile clips that went onto the test wire seemed to be the most likely ones that may have a poor electrical connection, for this reason the clips were squeezed tightly onto the test wire

All of the tests were then repeated and the results from the first combined and averaged out to improve the accuracy mathematically

Safety

Has with all experiments carried out in science labs, care should be taken at all times. Specially when working with electricity. I took care when touching the wires as they could be hot. I turned the power off at regular intervals to let it cool down. I also made sure the area I was working in was dry and there was no risk of water getting onto the wires, because this could be fatal when working with electricity.

First results ( nickel chrome wire )

Test results (first test) Swg 36

Test results (first test) swg 30

Test results (first test)Swg 26

Second results ( nickel chrome wire )

Test results (second test) Swg 36

Test results (second test)  swg 30

Test results (second test)Swg 26

Assessment      Average results ( nickel chrome wire )

Test results (Average) swg 36

Test results (Average) swg 30

Test results (Average)  swg 26

Analysis

I have completed my experiment, and I have found the results show that the resistance of the nickel chrome wire increases when the length of the wire increases and decreases when the thickness of the wire is larger, the lowest resistance was in the short thick wire and the highest resistance was in the longest thin wire.

Short thick wire – 40   inch of swg 26 wire = 0.31 ohms

Long thin wire   - 200 inch of swg 36 wire =  10.00 ohms

The trend shown in the results and displayed in the graph is clear and follows a almost straight line, as the length of the wire doubles then its resistance also doubles this is true for almost all the results, I believe all these results are reasonably accurate as they all follow the principal of ohms law. The pattern shown in the results graph is the same for each thickness of wire but it does get steeper as the wire gets thinner.

I conclude that the experiment and my results are explained by the number of free electrons being greater in a conductor with a larger cross sectional area compared to one with a small cross sectional area, this will allow more electrons to flow, giving a larger current flow for the same voltage. I also conclude that if the wire is longer it will require a grater force ( voltage ) to move the same amount of electrons than if the wire were shorter.

In my aim I set out to find why the electricity in my home is conducted in carried in large copper cables but the fuse wire that protects the circuit is only very small but carries the same current, this I can now understand because of the very small length of wire in the fuse it has a resistance that is only slightly more than the very long lengths of copper cable that provide power. It still has to have a high resistance than the cable because it must be the weak link in the circuit protecting it from overload.

Evaluation

I believe the experiment and its results prove the original prediction to be correct and show clearly that the resistance of the nickel chrome wire is proportional to its length, this table shows that as the length of the wire doubles from 40 to 80 the resistance also doubles from 0.63 ohms to 1.3 ohms the same is true for all the results, this can be explained because

the longer the wire the further the electrons have to travel and may collide with other particles, so increasing the resistance. The resistance is inversely proportional to its cross sectional area, the greater the area the more electrons are available the flow as current.

The method used was reliable but it could be improved by the use of more secure way to attach the leads onto the test wire, screw type connections for example, also the heating affect of the current flowing through the wire will also affect the result, I noticed that the wire that was being tested became very hot and had to be allowed to cool down between tests. This could be reduced by only applying the test voltage for a few seconds after all the connections have been made.