Introduction This investigation determines how changing the length of Nickel-Chrome (nichrome) wires, when passing an electrical current through them, affects their resistance. It also determines how resistance is affected by a change in the diameter of the wire used. Resistance is “the property of failing to conduct electrical or thermal energy”. Resistance is a force which opposes the flow of an electric current around a circuit so that more energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long, e.g. the filament across an electric light bulb.

Resistance is measured in ohms. A resistor has the resistance of one ohm if a voltage of one volt is required to push a current of one amp through it. George Ohm discovered that the emf (electromagnetic force) of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one, you triple the other. He also discovered that a circuit sometimes resisted the flow of electricity. He called this, resistance.

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He then came up with a rule for working out the resistance of a circuit: Vi?? I = R, V= Ii?? R and R=Vi??I V -Voltage (volts) I – current (amps) R – resistance (ohms) In conducting this experiment I examined the resistance of Nickel-chrome wire. I am investigating 2 variables that affect the resistance of the wire in this investigation. They are the diameter of the wire and the length of the wire.

This experiment queries the relationship between voltage, amps and resistance flowing through nickel-chrome wire with various properties. The results of both experiments will be compared and conclusions drawn about how the resistance changes, according to the length of the wire and the diameter of the wire.

A description of comparisons between the trends in the results of each experiment will be made and the ways in which the resistance of nickel-chrome wire changes as its length and diameter are adjusted, will also be evaluated. Before the experiment had begun, I predicted that concerning the first experiment, the longer wire the more the resistance and in the second experiment the thinner the wire the higher the resistance. This is because the electrons of a current flowing through short wire have less distance to travel and therefore have fewer collisions causing less resistance than they would get traveling further.

Collisions cause a loss of energy. In a thick wire they have more space to move around and are therefore less likely to collide with each other. (The more the electrons collide together, the higher the resistance. ) During each test in this investigation there were several factors that I needed to control or keep constant, to ensure that my results would be as reliable as possible. These included temperature of the wire and the voltage and current in the circuit. These are dependent upon the voltage input.

By ensuring that the voltage in each experiment is low enough that it does not heat up the wire and yet high enough that I can record clear readings, the test will be as fair and useful as it could be. The temperature contributes to the amount of resistance in the circuit. Therefore, I will have to keep it constant, to enable me to be sure that my results can be trusted. To reduce the chance that the wire is hot when tested, I made sure that I turned off all power in the circuit between each recording. This meant that the wire had less time to heat up.

By including an ammeter in series with my circuit, I will be able to record the amount of current flowing through it and check that it stays constant before each test. This will also enable me to calculate resistance. There was no change in current during the first experiment however in the second each diameter caused a change in current. This change was taken into consideration when I came to calculate resistance. By using the same voltage input, from the power pack each time in my investigation, I was also able to ensure that the voltage in the circuit was the same each time.

I also made sure that the external temperature was approximately constant throughout my investigation. It was necessary not allow the wires to build up heat. This is because in metal conductors, electrical current flows due to the electrons being transferred between atoms. As electrons move through a metal conductor, some collide with atoms or other electrons. (See diagrams on figure 1 on next page). These collisions cause resistance which generates heat. Heating the wire causes atoms in the wire to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance.

This increase in resistance changes the recordings of data by increasing potential difference and therefore increasing resistance. This would have make the test unfair and caused the results to be inaccurate and unreliable. This factor had to be controlled during each area of investigation. I took special care in deciding what voltage to use for each experiment because a large amount of voltage can cause the wire to heat up, causing resistance, however a voltage that is too low, can cause inaccurate or unclear readings.

The variable in the first experiment was the length, of test wire that is used in the circuit. The variable in the second part of the investigation was the diameter of 10cm of nickel-chrome wire. I chose these variables for this investigation because they can be manipulated in various ways as shown in the experiment. They are of reasonable complexity, with many variations to the experiment. The data once analyzed reveals many patterns and the equipment needed for this test was reasonably easy to get. Experiment 1 The purpose of experiment 1 was to examine how resistance is affected by a change in length of wire.

For this experiment, a factor that could affect the resistance of the wire, and which is not a variable in this experiment is the heat of the wire. This factor is a major reason for resistance in hot wires and is a factor which I am not intending to record the effects of, in this investigation. As described above, heat in a wire causes more resistance than if there was no heat. Therefore this factor will need to be controlled during the experiment (see figure 1 on page 3b, in the introduction section). This can be done by making the voltage as low as possible, without it being so low that a clear reading cannot be recorded.

Resistance in the copper wire need not be an issue, because copper is a very good conductor of electricity and transfers the electrons most efficiently. Method In the first experiment, I measured each recording of the test wire in exactly the same way to ensure that the test was fair. I measured the potential difference of the length of test wire. In order to do this, the conducting rod was placed at points along the wire. The conducting rod was fixed to the circuit at one end, and when connected to the test wire, created a complete circuit where the current could flow through the test wire.

The voltmeter displays the potential difference of the test wire. The points were recorded in stages of 10cm. I took 10 readings from 10cm up to 100cm (1m). This means that when the rod is placed only 10cm away from the beginning of the wire, the current only flows through that 10cm of the test wire. As the rod is moved along the test wire, more of the test wire is used by the circuit. Therefore, as more test wire is being used, the potential difference of the wire changes. I conducted the first experiment, to find out how changing the length of nickel-chrome wire affected its resistance.

To enable me to conduct this second experiment, I used the following equipment:  Power pack – as a supply of power  5 wires – to connect up the circuit and measure voltage An ammeter – to measure current A voltmeter – to measure voltage The 100cm length of nichrome wire attached to a ruler – to enable the length of wire to be calculated accurately, increasing reliability and accuracy. The circuit diagram below shows the circuit used in the experiment: CIRCUIT DIAGRAM 1 As shown, the ammeter was in series wire the circuit. This was necessary to give an accurate reading of current.

The voltmeter was used in parallel because I was measuring potential difference. The voltmeter measured the potential difference of the area of which it was in parallel with. Due to the fact that this experiment involves a long wire, I chose to use 10v DC in the circuit. This will ensure that a clear range of potential difference can be recorded from beginning to end of the test wire. Heat in the test wire at this voltage should not have been a problem, providing the power is turned off in between each recording to ensure that there is no gradual build up of heat in the test wire.

10v would ensure that potential difference could be accurately recorded right up to the end of the test wire. I did however make sure that the wire did not heat up during the experiment by feeling for heat. I also made sure that I turned off the power between each experiment to prevent any gradual increase in heat due to resistance. I only turned on the power for a brief moment to give me enough time to take the readings. I had an instant when I had set up the investigation wrong in this experiment and the circuit was not correct.

This caused a large amount of heat build up in the wire so much that it causes the wire to burn through the ruler which it was attached to and burned through itself causing it to break. This burning happed when the conducting rod was near the end of the wire. I later concluded that the reason for this was partly due to the fact that I was using such a high voltage, but mainly because all of the energy was being transferred into heat due to the resistance in the wire over a short amount of space. This is because there was only a short amount of nichrome wire that was being used to conduct the voltage.

This caused over heating due to the resistance. As heat increased, the rate that the wire was heating up increased because the extra heat was causing more resistance, causing more heat do be developed at a faster rate. To ensure that the results are as accurately, each reading will be taken 3 separate times and a mean will be calculated from them. This will improve the accuracy and reliability of the recorded data. By recording the current (using the ammeter) and potential difference (using the voltmeter), change in resistance can be calculated.

This data will be placed on a graph and analyzed. I will use various calculations to find the resistance of the wire (in Ohms), as different lengths of nickel-chrome are used. These include: Vi?? I = R which can be manipulated into V= Ii?? R. The drawing (figure 1) shows the circuit diagram. In my prediction I stated my opinion that resistance should increase as the length of the wire increases. After conducting the test, I found that my prediction was indeed correct and there was a clear trend which showed an increase in resistance at a steady rate. The graph shows this trend.

Analysis of Experiment 1 This table shows the potential difference of various lengths of nichrome wire when included in the 10v circuit: 0. 56amps Potential difference (V) (2d. p. ) To show how the resistance was calculated, here is an example of the process of calculating resistance. This calculation was for the first recording of the mean of 10cm of wire. I used the formula, Vi?? I=R. (1. 00+0. 97+0. 93) i?? 3 = 0. 97 (mean). 0. 97(voltage) i?? 0. 56 (amps) = 1. 7(ohms). These tests were done using a 1m length of wire with a diameter of 34mm.

I chose to use 10v of voltage because it gave the clearer results than a lower voltage because the numbers where higher. I made certain that this voltage did not heat up the wire. I felt the wire and found no heating effect. Therefore there was little additional resistance caused by the temperature of the wire. I originally chose to record the results for this experiment using 3 decimal places (3d. p. ) however due to an error in the recording of current in this experiment; the only data available is resistance to 1d. p.

The error in this experiment was a small and single mistake but one which had a huge affect on the results. When I was recording the current for this experiment, it is most likely that I either misread the ammeter when recording current (56amps instead of 0. 56amps), or it could have been a typing error. I may have entered 56amps into the table instead of 0. 56amps. I chose to use the results to 3d. p. because I realized the mistake, the results for resistances were all in decimal places, and therefore the significant figures were all below the decimal point.

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