Look at the various lengths of Constantine wires and observe how their lengths might affect resistance of a wire.

Resistance of wire.

AIM: the aim of my investigation is to look at the various lengths of Constantine wires and observe how their lengths might affect resistance of a wire.

BACK GROUND INFORMATION:

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

All conductors have some resistance but;

Long wires have more resistance than short wires;

Thin wires have more resistance than thick wires;

The resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and the voltage across the wire (in parallel). These measurements are then applied to this formula:

V = I, R. Where v is voltage, I IS current and R is resistance.

This is calculated using

VOLTAGE

RESISTANCE = CURRENT

The unit of resistance is the ohm ( )

For example;

If there is a voltage of if there is a voltage of

12 volts across this piece 12 volts across this piece

Of nichrome wire, then of nichrome wire then

A current of 4 amps flows a current of 2 amps flows

Through so; through so;

Resistance = 12/4 ohms resistance = 12/2 ohms

= 3 ohms ...

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A current of 4 amps flows a current of 2 amps flows

Through so; through so;

Resistance = 12/4 ohms resistance = 12/2 ohms

= 3 ohms = 6 ohms

So, the higher the resistance, the less the current flows for each volt across the wire.

Current through a metallic conductor (e.g. wire) at a constant temperature is proportional to the potential difference (voltage). Therefore V ¸ I is constant. This means that the resistance of a metallic conductor is constant providing that the temperature also remains constant. Furthermore, the resistance of a metal increases as its temperature increases. This is because at higher temperatures, the particles of the conductor are moving around more quickly, thus increasing the likelihood of collisions with the free electrons.

The volt meter measures the voltage across the wire. The ammeter measures the current flowing through. The water keeps the wire at a steady temperature.

Predictions

I predict that the longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal. Therefore, more energy is going to be lost in these collisions (as heat).

Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire one is also doubling the collisions that will occur, thus doubling the amount of energy lost in these collisions.

EQUIPMENTS;

Crocodile clips, constantane wire, meter rule, plastic rod, ammeter, voltmeter, H2O, beaker,

Method

The following circuit was constructed to perform the investigation:

The two ENDS ( ) represent the crocodile clips that were placed at the ends of the required length of wire.

During this investigation I will be observing the change in resistance of different lengths of Constantine wire which are; 70cm, 65cm, 60cm, 55cm, 50cm, 45cm, 40cm, 45cm, 30cm, 25cm.

I will measure 70cm of contantane wire with a meter rule, cut it and wrap in coils round a plastic rod (a metal alloy).
I will place the crocodile clips one at each ends of the constantane wire
Then I will put the wire and the rod into a solution of H2O. Making sure the whole wire was in the water so that we have the accurate result and a fair test.
The power supply is then turned in and the volt and current are read of the ammeter and voltmeter. Then record the information.
The power supply in then turned off.
I will repeat this for the lengths of 65cm, 60cm, 55cm, 50cm, 45cm, 40cm, 35cm, 30cm, 25cm, by moving the crocodile clips to the next length, and so on.

The entire investigation is repeated again for accuracy.

FAIR TEST:

To make this investigation a fair test,

I will, make sure that all the pieces of coiled wire is inside the solution of H2O .make sure I let the wire to cool down after each investigation as the heat from the previous can affect the result of the next, and also make sure the appropriate measurement at each stage is taken to avoid any anomalities.

SAFTEY

In order to perform a safe experiment, a low voltage of 1V was chosen so that overheating was minimised. Furthermore, lengths lower than 25cm were not tried, which also helped to avoid overheating

RESULT TABLES:

Trial One

In order to decide upon the voltage and lengths of wire to use in the final experiment, the following rough trials were carried out:

The experiment was then repeated again to be assured that our results are accurate.

TRIAL two

This is the result:

After performing these trials, we plotted graphs to compare our results and it was then decided that the second trial will be used as our proper experiment as it had more accurate result and no anomalies.

CONCLUSION AND ANALYSISG EVIDENCE

Having performed the investigation, the following conclusions were drawn

As predicted, an increase in length resulted in an increased resistance. This can be clearly said for both attempts

Both wires show a strong trend of a straight line, i.e. the length of the wire is shown to be directly proportional to the resistance – double the length and the resistance doubles

After the experiment, I noticed that in my result, the resistance was decreasing by 2 and 3.

My prediction was correct because the resistance of the wire was decreasing each time we took 5cm from the wire.

The overall resistance of the two wires seems to differ considerably. Due to the strong correlation of the results, the explanation of this is unlikely to be the method used to obtain the results. The more likely explanation would be that the first wire was not let to cool down after each before doing the second test. So I did not obtain a fair test in this one. Obviously this is a rather important oversight and this will be discussed more in the Evaluation section.

EVALUATION

As mentioned previously, the biggest downfall of the investigation was the apparent mistakes when using the first wire because I did not let it cool down before I carried on with my investigation. So the heat released through the wire was carried on into the next there by not given a fair result because it was using the already exisisting heat.

Generally speaking, wire 2would appear to contain the most accurate results due to the fact that all of its points bar one sit on the line of best fit for that wire. The only one that does not is the point at 55cmwhich was exactly at the point were there was a slight anomality.

Wire 2, on the other hand, two main anomalous results at points 25 and 35.They are by no means that far off but in an experiment such as this, which is generally a very accurate one anyway, such anomalous results should not be quite so common. Possible explanations for these anomalies are as follows:

The length of wire for that particular measurement was not correct. At 25, 35 it is possible that the length was shorter, causing a lower resistance, and at 20 it is possible that it was longer, causing a higher resistance. The solution to this is to measure the lengths more carefully and ensure that the wire is pulled tight against the metre rule.
For a particular result, I think it was because the wire was not let to cool before carrying on the next step of my investigation.

Whilst extremely unlikely, it is conceivable that the power supply was providing a different voltage for some of the results. This is unlikely to be a problem in this investigation but it might have been an issue had we used batteries instead.

So in order to avoid all these anomalities, I will adjust my method by leaving each wire to cool down for 2 mins after each procedure, checking that I have the correct length of constantane wire by measuring it twice or more, and do the investigation again using a battery instead of the normal power supply and compare the result as I feel it had a part in the inaccurate result.