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Resistance of a Wire Investigation

Extracts from this document...



Before starting my coursework I have decided to choose a factor that will affect the resistance of a wire. I shall do this by going through all of the factors that affect the resistance of a wire and how I would measuring each factor to find out which would be the most effective and easiest factor to measure. Below is a list of factors and reasons why they affect the resistance of a wire. From this list of factors I  shall only pick one factor to investigate. To explain the how the factors would affect the resistance of a wire I have drawn a diagram to show how resistance occurs.


To chose which factor I am going to investigate I am going to consider how I would measure each factor and which factor would be the best and easiest to record. To measure the wire width I would use different widths of the same length and same material of wire. To record the difference in widths I would use the same voltage and measure the resistance for each thickness. Although it would be easy to obtain and record the data the graphs that I would be able to draw up would not be interesting. For the temperature of the wire I would not be able to carry out a fair test because it is extremely difficult to produce and control the range of temperatures needed without the correct equipment. If I chose to measure the difference in the resistance in different materials I would chose a number of different materials and using the same voltage I would record the resistance given by each wire of the same length and width.

...read more.


















Wire 2, Set 2:

Length (cm)

Voltage (V)

Current (A)

Resistance (W) (to 2 d.p.)









































Averages for each wire were then calculated to give these results, which were then graphed:

Length (cm)

Resistance (W) (to 2 d.p.)

Wire 1

Wire 2

































As mentioned previously, the biggest downfall of the investigation was the apparent mistakes when choosing the wire, in that they would appear to be of differing diameters. This did not, in this case, cause a big problem as the same wire was used for each set of results so it is known that the results for each wire are correct.

Wire 1 would 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 90cm, which was exactly at the point that the black mark (mentioned previously) was found to be.

Wire 2, on the other hand, had three main anomalous results: at 50, 80, and 90cm. 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 50 and 80cm it is possible that the length was shorter, causing a lower resistance, and at 90cm 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, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then. If it is higher than it should be then the connections could be cleaned.

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.

NB:      If one were to assume that Ohm’s Law applies, then another possible explanation could be that at some points (more likely in the lower lengths), the wire was not allowed to cool completely so that the temperature was higher for that measurement. Whilst unlikely (due to the two sets of results), this would cause a higher resistance as explained previously. However, it is now known, after researching the metal alloy “constantan,” that the resistivity (the electrical resistance of a conductor of particular area and length) of this alloy is not affected by temperature. Therefore, in these experiments Ohm’s Law does not apply.


The four factors that affect the resistance of a piece of wire:

  • Length,
    Diameter, or thickness,
  • Temperature and
  • The type of metal.
  • From thinking about how I would do this investigation and the outcome of it, I decided to use the length of the wire as the variable.


Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this, the length increase should be directly proportional to the resistance increase. To measure and record the results for this factor is simple; the results would be collected and could show a connection between the length of the wire and the resistance given by the wire. This is why I have chosen to investigate how resistance changes with length.

Ohms law, V=I/R. This says that for a certain current (charge flowing at a certain rate), there will be a greater voltage across the wire if it has more resistance. This tells me that the voltage measures the amount of energy used up in getting each coulomb of charge through the wire. The units of volts are the same as joules per coulomb. Therefore, Ohms law says the more resistance means more energy used to pass through the wire. Resistance is a measure of how much energy is needed to push the current through something. The electrons carrying the charge are trying to move through the wire, but the wire is full of atoms that keep colliding in the way and making the electrons use more energy.

Preliminary Method

In this preliminary experiment, I will use different lengths of wires to measure their resistance. The main idea of doing the preliminary experiment was to find a suitable current number to put the power supply on. I also wanted to do this experiment to familiarise myself further with the method; if I had any problems I could correct them there and then. This would mean I would obtain precise and reliable results in my main experiment when investigating the connection between the length of the wire and the resistance of the wire. First, the circuit was set up as shown below. I had to be careful in connecting circuit, because the Voltmeter had to be placed in parallel and the ammeter, which had to be placed in series. Draw up a rough table onto a piece of paper with the appropriate headings. The wire was cut to just over 50cm so the crocodile clips could attach onto the wire, making the results more accurate. Stretch out the wire onto the bench and measure with a metre rule. The power supply was put on 2V and the gradually increased the 4V, to find a suitable current for my main method. The slider on the resistor was moved to allow me to do five repeats. I decided to go down in ten centimetre gaps, as it would allow me to lot a graph of resistance against length with a range of fie readings.


As shown below there is only a range of five readings, which start to show a pattern, that the best fit line is directly proportional? To see if this trend carries on, I will widen my main experiment and use a 100cm length of wire, I will also take the readings every 5cm and not 10cm. From my experimentation with the power supply, I have decided to keep it at 4V, as I do not need the wire length to go lower than 10cm.  

Main Experiment


I predict that if the length increases then the resistance will also increase in proportional to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Therefore, if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph should show that the Length is directly proportional to the resistance.

If the length of the wire is only half the length of the wire on the same type of wire, there should be half the number of collisions between the electrons and the atoms. If the wire is twice as long, there should be twice the number of atoms, resulting in twice as many collisions and a predicted doubling of the resistance.


Handle the power supply carefully. I am going to only use a voltage of four volts so the wire will not burn. Be careful when touching the wire, as it may be hot. Start on the lowest current, so the wire then will not melt or burn instantly. Be careful when the wire is connected, as it will get hot. Be careful when cutting the wire. Make sure the mains to the power supply are switched off when removing the wire from the circuit to be measured.


Power Supply,



Just over 100cm of E26 Wire,

Meter Rule,

Two Crocodile Clips,

Connecting Wires.

Factors which must stay constant to keep the experiment a fair test:

  • The power supply must stay on 4V,
  • The wire must be the same thickness,
  • The surrounding temperature must be constant,
  • The equipment should be kept the same,
  • The edge of the crocodile clips should be at the edges measured length.

The Variable factor

The factor that I am going to vary is the length of the E26 wire.

Circuit diagram


The circuit was set up as shown above. A table was drawn out and the results were recorded. To improve the accuracy, compared to my preliminary results for my main Experiment, I have decided to set up the circuit with the metre rule sellotaped to the bench. This will make it easier and more precise as I will not have to keep on holding the wire then putting the crocodile clips on. I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller ruler and the meter ruler can be accurate to + 1mm. Make sure that the metre rule is actually one metre long and not one or two centimetres shorter. Next, move the crocodile clips down five centimetres rather than ten (as done in preliminary) each time to record the results. Use the E26 wire as it will also be easier to measure any change in resistance. To collect the data for my graph I have chosen to take a range 20 of lengths. I have chosen a range of 20 as to plot an accurate graph, I will need at 20 points to mark on the graph if I want to make precise and reliable results, to see if there are any patterns and trends. I have also chosen to take five repeats at each length and then take an average, to get reliable results. The lengths that I have chosen are as follows: 100cm, 95cm, 90cm, 85cm, and going down in fives to 10cm length of wire. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results.

As my preliminary results start to show a pattern in the readings (Resistance is directly proportional to length) to expand on my experiment and to see if this pattern continues, I am going to try the above lengths.


To calculate the resistance of the wire, I shall use the equation below.


In my prediction, I stated that:

If the length increases than the resistance will also increase in direct proportion to the length. From my graph on the previous page, I can see that the resistance of the wire is directly proportional to the length of the wire. I know this because the Line of Best Fit is a straight line through the origin showing that if the length of the wire is increased then the resistance of the wire will also increase in proportion to each other. The line of best fit is a straight and it goes though (0,0) if there is no length, there is no resistance proving that the resistance of the wire is directly proportional to the length of the wire. This proves my prediction right. I can work out the gradient of this line by dividing the Resistance by the length. So, 1.75/55=0.0318

The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.

The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions that will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased, the number of atoms will also increase.

If the wire is half the length of a certain wire, it would have has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times. In addition, if the length of the wire was trebled or quadrupled, then the resistance would also treble or quadruple. This is indicated on my graph, with the length being 100cm and the resistance being 3.25 Ohms. This in theory would mean that at 50cm there would be a resistance of 1.63 Ohms. From the graph it is easy to tell that the theory is correct and therefore my results reliable. From my results table and graph, I can see that my results that I collected are quite reliable and accurate. I know this because my results table shows a few, individual anomalous results; the anomalous results are at lengths 95cm and 100cm. All the other points are extremely close to the line indicating that my results are accurate. I think that my results are suitable to confirm my prediction and support a conclusion. I know this because outside resources (Textbooks and Britannica) say that ‘the length increases in direct proportion to the resistance.´



I am going to be studying the resistance of wire. The purpose of this investigation is to see how length and thickness of wire affect the dependent variable, resistance.


I predict that, as the length of the wire doubles, the resistance will also double, but as the cross-sectional area of the wire doubles, the resistance halves. This means that the length will affect the resistance more than the thickness will.


Electrons bumping into an ion causes resistance. If the length of the wire is doubled, the electrons bump into twice as many ions so there will be twice as much resistance. So if the cross-sectional area of the wire doubles there will be twice as many ions and twice as many electrons bumping into them, but also twice as many electrons getting through twice as many gaps. If there are twice as many electrons getting through, as there is twice the current, the resistance must have halved. This means that

I am assuming that the temperature is kept constant and that the material is kept constant. We can include this in our equations by adding a constant


Equipment needed:

  • 1 x Power Pack (to give varied voltage)
  • 1 x Voltmeter
  • 1 x Ammeter
  • 5 x wires (with crocodile clips)
  • Wire of varied length and thickness
  • Controlled variables:
  • Temperature (room temperature)
  • Wire material
  • Dependent variable:
  • Resistance
  • Independent variables:
  • Thickness of wire
  • Length of wire

Circuit diagram

First, set up the experiment as shown above. Turn on the power and set the power pack so that the voltmeter reads 0.1 volts. Take the reading from the ammeter recording both the current and the voltage. Then do the same again but use voltages of 0.2 volts, 0.3 volts, 0.4 volts, and 0.5 volts. This is so that when we work out the resistance (V/I) we will have five readings and can then take an average resistance. Then carry out the whole thing again, varying the length of the wire in intervals of 10cm from 10cm to 100cm.

To do the thickness experiment, set up the equipment again as shown. Turn on the power and set the power pack to read 0.2 volts. Take the current reading then turn off the power and start again. Take four readings like this so that an average resistance can be found. Next, change the thickness of the wire and do the experiment again. Use the diameters 0.71mm, 0.56mm, 0.28 mm, and 0.20mm. Although the diameters haven't the same interval between them, once we have worked out the resistance, we can draw a graph to discover any relationship between the thickness and the resistance of wire.



Photosynthesis is the chemical process, which takes place in every green plant to produce food in the form of glucose.  Plants use the suns energy to join together water and carbon molecules to make the glucose, which is sent around the plant to provide food.  Cells in the root or stem can use the glucose to make energy, if the plant does not need to use all the glucose immediately then it is stored which is difficult because glucose is hard to store in water.  Plants solve this problem by joining hundreds of glucose molecules together to make starch.  Starch does not dissolve in water very well so it makes a better food store.

  Photosynthesis takes place mainly in leaves and depends on an important green pigment called chlorophyll, which is found in chloroplasts.  To obtain the most sunlight as possible, leaves have a large surface area and the more sunlight the plant receives, the better it can photosynthesise.  Chloroplasts are found in palisade cells in large numbers and to allow as much light to get in as possible, the cells are arranged like a fence.  This helps the energy entering the surface of the leaf to travel a long way through the palisade cells.

  Glucose can provide energy or carbon, which can manufacture other molecules in the plant.  Which can make new living matter and this is called biomass.

  The chemical equation for photosynthesis is:

            Carbon dioxide + Water    =   Glucose and Oxygen

            6CO2  +  6H20  =  C6H1206  +  6O2

Key Factors:  CO2 is vital in photosynthesis because the plant takes in CO2 from the air and joins with water molecules to make glucose.  The CO2 comes in through the stomata pores on the surface of the leaf and only 0.03 % of the air around is CO2 so it’s pretty scarce.

Temperature has to be kept at a certain level because if it gets too hot, about 45`C then the enzymes in the chlorophyll will be killed and photosynthesis will stop altogether.  If the temperature is too cold then temperature becomes a limiting factor and the enzymes will stop working.

Light As chlorophyll uses light energy to perform photosynthesis; it can only do it as fast as the light is arriving.  Chlorophyll only absorbs the red and blue ends of the visible spectrum but not the green light in the middle, which is reflected back.  If the light level is raised the rate of photosynthesis will increase steadily but only to a certain point.

Water is important because it is needed to join with CO2 molecules to make glucose and the amount of chlorophyll needs to be enough so that the plant can photosynthesise to the best of its abilities.



I predict that the plastic sheets coloured green, yellow, and orange will produce the least amount of bubbles because the light will be transmitted.  Whereas placing red and blue sheets in front of the Elodea will result in the greatest amount of bubbles because the light is absorbed.  Certain colours of light can limit the rate of photosynthesis depending on how well it is absorbed into the plants chlorophyll to photosynthesise.  In addition, the wavelength can change the rate of photosynthesis.  If the lamp supplying heat for the plant were placed twice as far away, I predict that there would be half as many bubbles.  In addition, if it were moved twice as far closer then there would be twice as many bubbles.  This is backed up with knowledge from previous experiments and ones done by other people and scientific understanding.


Previous experiment 


For our experiment we chose as accurate equipment as possible to give us the most accurate results.  The equipment is as follows: 

  • 1 lamp A boiling tube
  • A small piece of Elodea Plastic
  • Sheets of different colours
  • A beaker

The boiling tube was filled with water and the Elodea placed in.  The boiling tube was placed in the beaker and the lamp placed at a set length away.  He plastic sheets were individually wrapped around the beaker with an elastic band.  For every new plastic sheet we counted the number of bubbles each time for a minute.  It was important to keep the experiment the same each time to ensure it was fair test for example: The lamp stayed the same distance from the beaker, we used the same plant each time, and the plastic sheets were all the same size.  The experiment was repeated three times and the results were averaged to ensure they were regular and as expected.  Results were recorded each time and patterns observed.  Previous results for an experiment of this kind have been recognized and compared.  Throughout the experiment we observed for a number of distinctive things:                                                

  • Increase/Decrease in bubbles                                       
  • Temperature Increase/Decrease
  • Change in Elodea
  • Size of bubbles

Variables include: 

  • Length of Elodea
  • Amount of water
  • Distance of lamp
  • Size of boiling tube
  • Transparency of sheets
  • Time spent counting

Changing either of the variables would have had effects on the results; we kept ours all the same each time to ensure a fair test. 


As predicted, the results conclude that using sheets with colours near the red and blue end of the spectrum produce a higher amount of bubbles than those near green.  Thereby proving that photosynthesis is increased with certain colours of light.


In observation of the results, I have seen how the rate of photosynthesis in the Elodea has been affected by the various factors.  In reference to the prediction, I was correct in that the red and blue coloured sheets produced the highest rate of photosynthesis, whereas the sheets, which were green and yellow, resulted in the least bubbles.  I feel that we had taken enough measurements to be sure of a fair test as the experiment was repeated several times so.  Each plastic coloured sheet we used had the same time, and variables as the others so we obtained precise results for every test.  We did not find anything, which stood out too much from the pattern except that the red plastic sheet, when used resulted more bubbles generally than the blue sheet.  This shows that chlorophyll absorbs red light more easily than blue.  We acquired similar results with each repetition and found ours to be similar to previous experiments.  The Elodea produced more bubbles with sheets at each end of the spectrum because the chlorophyll in the plant absorbs all the colours but transmits green.  When the light is absorbed the plant converts it into energy to photosynthesise.  The more light energy it receives the better and faster it can do this so when the sheets near the blue and red parts of the spectrum are held in front of the Elodea it absorbs the light and can photosynthesise better.  If plastic sheets are held up which are have a colour near the green part of the spectrum then the light will be transmitted and the plant will not be able to photosynthesise as well.  In this experiment we have covered the main colours of the visible spectrum and they are sufficient to produce the results that we are looking for.

If we were to repeat the experiment then there are several ways we could improve it.  For example to get around the problem of the heat from the lamp producing more bubbles then a thick glass panel could be placed in the middle to prevent any heat reaching the Elodea.  To improve the accuracy of counting the bubbles, you we could only count the ones, which are a certain size, and only the ones coming from the very end of the Elodea.  If there were lots of people counting the bubbles and the results averaged then that would be a more accurate way of obtaining the information necessary.  To extend the investigation you could change certain variables for example the type of plant that you are using to count the bubbles from.  You could try an entire species of plant and see if the results are similar for every type. You could use different chemicals in the water each time to see which chemicals result in the greatest rate of photosynthesis.



The aim of my experiment was to determine whether or not the intensity of light would affect the rate of photosynthesis in a plant. To do this, I placed a piece of Canadian pondweed in varying light intensities, and observed the amount of oxygen being given off. I used Canadian pondweed because of its unusual quality of giving off bubbles of gas from a cut end, when placed in water.


Photosynthesis occurs only in the presence of light, and takes place in the chloroplasts of green plant cells. Photosynthesis can be defined as the production of simple sugars from carbon dioxide and water causing the release of sugar and oxygen. The chemical equation for photosynthesis can be expressed as:


6CO2  + 6H2O  A  C6H12O6 + 6O2  (in the presence of chlorophyll)

The fact that all plants need light in order to photosynthesise has been proven many times in experiments, and so it is possible to say that without light, the plant would die. The reason that light intensity does affect the rate of photosynthesis is because as light, and therefore energy, falls on the chloroplasts in a leaf, the chlorophyll, which then makes the energy available for chemical reactions in the plant, traps it. Thus, as the amount of sunlight, or in this case light from a bulb, falls on the plant, more energy is absorbed, so more energy is available for the chemical reactions, and so more photosynthesis takes place in a given time. There are many factors, which affect the rate of photosynthesis, including light intensity, temperature, and carbon dioxide concentration. The maximum rate of photosynthesis will be constrained by a limiting factor. This factor will prevent the rate of photosynthesis from rising above a certain level, even if the other conditions needed for photosynthesis are improved. It will therefore be necessary to control these factors throughout the experiment so as not to let them affect the integrity of my investigation into the effect of light intensity.


I predicted that as the intensity of light increased, so would the rate of photosynthesis. Furthermore, I hypothesised that if the light intensity increases, the rate of photosynthesis will increase at a proportional rate until a certain level is reached, and the rate of increase will then go down. Eventually, a level will be reached where an increase in light intensity will have no further effect on the rate of photosynthesis, as there will be another limiting factor, in this case probably temperature.

Preliminary work

Initially, to ascertain a suitable range of distances at which to record results for my experiment, I did a preliminary investigation in which I recorded the number of bubbles of oxygen given off in a given time at various light intensities. To alter the light intensity, I placed a lamp at various distances from the plant. I also therefore needed a way of accurately measuring the light intensity, and I did this using a photometer. I recorded the lux reading (unit of light intensity) at each distance. I got the following results:

Results of preliminary experiment


Light intensity

No. Bubbles






























...read more.


2 and H2O can react. The chlorophyll can only absorb up to a certain amount of light, and so when the light intensity reaches a certain point, any increase in light intensity after that point does not affect the reaction; it stops being a limiting factor.

A Chloroplast

While doing the experiment thrice contributed to the accuracy of the experiment, there were factors that detracted from it. The method of measuring the rate of photosynthesis by the frequency of bubbles was one. The volume of the bubbles could have varied, meaning that a larger or smaller amount of oxygen could have been released without being recorded. Also, the distance between the light source and the beaker could have been slightly longer or shorter than was recorded, making the light intensity less or more than was expected. To remedy these things, I could have used apparatus like a micro-burette or some other tool for measuring small volumes of gas. This would make the results more accurate. To correct the problem of inaccurate distance measurements, a variable wattage lamp could be used so that as the wattage increases or decreases so to does the light intensity. These inaccuracies however do not seem to have affected the results, as can be seen from the shape of the graph.

Other experiments in this area could include testing the rate of photosynthesis under different temperatures, as the sun could be giving the plant heat as well as light as an energy source; testing the rate of photosynthesis with different water to CO2 ratios; and also testing the rate of photosynthesis with different amounts of chlorophyll in the plants.

...read more.

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