I predict that if I double the length of the nichrome wire, its resistance will also double. I predict that if I half the length of the nichrome wire, the resistance will also half. Therefore I predict that resistance will increase in proportion to the increase in the length of the wire.
HYPOTHESISWhy does a metal conduct?A metal is made up of positive ions surrounded by a sea of free electrons. The ions in a metal are positive because it is easy for a metal to lose one or two electrons, from its outer shell, than to gain six or seven electrons to complete the outer shell. The electrons are lost and are free to move around and the ions become positive as the number of protons increase, compared to the number of electrons. The metal can now conduct electricity, as it is positive.Here is a diagram to show the structure of a metal:What is resistance?Resistance is the measure of how difficult it is for the current to get through a wire. We measure the resistance in Ohms, with the symbolResistance, R = p.
d. across the wire (V)___Current through the wire (I)R = VIWhat causes the resistance in a wire?The electrons in a wire are free to move through it, but it is not perfectly easy. The ions of the wire get in the way. The electrons collide with the ions and get slowed down. So a single electron will make a stop/start journey along the wire as it bumps into ions. The piece of wire has resistance because the ions restrict or resist the flow of electrons.Ohm’s Law states that, ” The current flowing through a metal wire is proportional to the potential difference across it.” (Providing the temperature remains constant.
) ‘Proportional’ means that if you double the p.d. the current is doubled. Therefore the current is inversely proportional to the resistance. Whatever we do to the resistance, it changes the current by one over the number.Voltage =Current*Resistance I.
RResistance =Voltage R = VCurrent ICurrent =___1____ I 1Resistance RThis supports my prediction that if I double the length of the wire, the resistance will also double and if I half the length of the wire, the resistance will also half as I am going to change the length of a wire while carrying out this investigation.Resistance restricts the amount of current flowing through a wire and therefore slows down any reaction, which it supports. Resistance also plays a good part as it stops things from blowing.
It stops too much current from getting through, which can blow or damage an appliance.Four factors affecting resistance are:1. As the length increases, the resistance increases. This happens because if the length of a wire is increased the electrons will have to pass through more ions without colliding.
That rarely occurs and resistance increases as they collide. This can affect the results of my experiment as I have to decrease the length of wire in my experiment and if I make an error in decreasing the length, it can change the results of the whole investigation.2. As cross-sectional area increases, the resistance decreases.
This is true because, if there is more cross-sectional area for the electrons to flow in, there is a better chance that they will get through without colliding. As a result resistance will decrease. This will not affect my investigation, as I will be using the same cross-sectional area of wire throughout the investigation.
3. Only good conductors are used for connecting wires. Good conductors such as copper are used to connect wires as they have got a low resistance and will allow more current to flow through them. Very good conductors such as gold improve the quality of output of an electric appliance. The wire, which I am using in the experiment, is nichrome, which is a good conductor.4.
As temperature increases, the resistance of a wire increases. As the temperature is increased the ions vibrate more vigorously, colliding with electrons, which are moving through the wire, producing heat energy. The increasing temperature favours more collisions, and the collisions restrict the amount of current flowing through. Therefore resistance increases. This factor will not affect the investigation, as I will be doing the investigation at room temperature.The length of a wire affects resistance because:In theory I conclude that the smaller the wire, the less resistant it is. The bigger the wire the more resistant it is. This also supports my prediction that if I double the length of a wire the resistance will also double.
Apparatus required:; Power supply 0-12V (dc); 1 m nichrome wire; Ammeter; Voltmeter; Connection wire; Metre rule; Crocodile clipsHere is a circuit diagram for the experiment I am going to carry out:VariablesIndependent variables are the factors that I will change during the experiment. In my Investigation the independent variables are:; Length of wire in cm; VoltageDependant variables are the factors that depend on the independent variables. In the investigation the dependant variables are:; Resistance; Current; TimeControl variables are the factors that must stay the same to make it a fair test. The control variables are:; Temperature; Type of material (wire); Thickness or cross-sectional area of wire.I must keep all the control variables the same throughout, as they will all restrict the amount of current flowing through, if changed during the experiment.
Therefore they will all increase the amount of resistance and I wont be able to obtain accurate results.Method; I will set up the apparatus as shown in my circuit diagram above on page 3.; I will decrease the length and increase the voltage as I carry out my experiment.
The range of measurements in my investigation are as follows:100cm-20cm this measurements are reduced in 10cm intervals and I will take 9 readings. I am only bringing down the length of the wire to 20cm so as to avoid over heating of the short wire in a high voltage.The voltage is increased from 2volts to 8volts in 2-volt intervals. Therefore I will take 4 readings for each measurement.
The limit in the investigation is 8 volts so as to avoid over heating and burning the wire. If the voltage were higher than 8 volts for this type of wire, then it would burn the wire and ruin the whole investigation.; I will then record the current readings obtained and find the Resistance using the formula: R=VI; I will then find the average resistance by dividing the total resistance of all 4 different volts by 4.
In my investigation I will have to cool the wire after increasing the voltage each tine so as to obtain accurate results. High voltage can also burn the wire so I will have to cool the wire for safety reasons.High voltage increases the temperature in a wire and therefore also causes more resistance because the ions and electrons gain more energy and vibrate more vigorously causing collisions, hence more resistance as the electrons are blocked from reaching their destination.I will repeat the whole experiment once again to make my results as accurate as possible.SafetyWhile doing the investigation, it is important to keep safety into consideration. The scissors should only be used for cutting the wire to the appropriate length and for no other reason. Before using the power pack, the pointer should point at 0 volts.
It is important to be careful while using the power supply. While handling live wires, it is essential to be careful. The voltage should be kept low because of the safety factor and the wires heating up.OBTAININGResults table 1 showing the readings obtained after carrying out the experiment.
Length (cm)Voltage (V)Current (A)Resistance ( )Average Resistance ( )10020.623.23184.108.40.2061.93.
74680.72810.750.74I used the formula R=V to calculate the resistance.
ITo calculate the average resistance I added up the resistance for each measurement and divided the total by 4.Results table 2 showing the readings obtained after carrying out the experiment.Length (cm)Voltage (V)Current (A)Resistance ( )Average Resistance ( )10020.693.393.3941.
8644.720.8567.10.8589.20.87AnalysingHere are the graphs showing the results from the result tables.Overall the investigation, I carried out went quite well and my results are also fairly accurate.
For example in my first result table, when the length of the wire was 50cm the average resistance was 1.64 . When I doubled the length to 100cm the average resistance also almost doubled to 3.18In the second table, when the length of the wire was 20cm the average resistance was 0.86 . When I doubled the length to 40cm the average resistance also almost doubled to 1.
50. My graph of average results also shows that all the points are almost in the line of best fit. This also proves that if I double the length of a wire the resistance will also double.This shows the evidence that the resistance is directly proportional to the length of a wire. ‘Directly proportional’ means when a substance doubles the other substance also doubles. The evidence I found also backs my prediction that if I double the length of a nichrome wire, its resistance will also double.
The resistance will double because the ions will restrict or resist the flow of electrons and therefore creating resistance as a result of collisions between the ions and the electrons.EvaluationAfter carrying out the full investigation I can say that my results are quite reliable and agree with my prediction that I made.Overall there were no anomalous results in my investigation as you can see from my graphs, but my results are not also perfect as in my theoretical prediction. Errors may have occurred while I was doing the experiment.
Here are the errors, which may have occurred while I was doing the experiment. There are two types of errors namely:; Systematic error-this is the type of error due to the fault in a measuring device.; Random error-this is the type of error due to human mistakes.Systematic errors in my investigation are:; The ammeters and the voltmeters were probably faulty and I could not get the accurate results.; The power pack might have malfunctioned and might have ruined whole of the voltage supply.; The scale of the metre rule I used was not marked according to scale and that affected in the accuracy of my results.The random errors:; I might have made a mistake while recording the results.
E.g. instead of recording 3.06 I might have recorded 3.66; I might have cut the wire a little longer or a little shorter while cutting it.Due to all these errors the accuracy of my results might have been brought down while doing the investigation.The ways that I could improve this method to get more reliable data are:; Using computer controlled ammeters and voltmeters to detect any faults n them.; Use a more reliable power pack then the one I used in the investigation.; Use a different piece of wire for each length so as to prevent over heating of the wire.; Use a digital ruler to measure the different lengths of wire to prevent the measuring error.These are the ways, which I came across in order to get more reliable and precise results.Further experiments that I can do to investigate this topic are:; Measuring the resistance in a bulb using different volts; Measuring the amount of resistance in metals such as copper, with different masses.Doing these experiments will further prove my results more reliable and back the theory of resistance.