Using this theory, it seems that the resistance of a wire can be quantified, because it seems that if an electron has to pass twice as many ions as in the original wire then the electron will collide with twice as many ions and will, consequently knocked off course twice as many times with the result being that the electron takes twice as long to travel through the wire. Doubling the length of wire doubles the number of ions in the wire and therefore it will take an electron twice as long to go through a piece of wire twice as long.
In a similar manner, it will take an electron three times as long to travel through a wire three times as long. This can then be applied to a piece of wire ‘x’ times as long as the original wire because we can see that it will take an electron ‘x’ times as long to pass through a wire ‘x’ times as long (on average). Thus, we can deduce that: R = x L (‘x’ is a constant) Evaluation The think that the experiment performed was successfully as there were no anomalous results plus the results produced a perfect line of ‘best-fit’.
The fact that there we no anomalous results shows that the method was suitable and was carried out accurately. It also suggests that the points mentioned in the preliminary work – regarding leaving the power supply on for the minimal time to keep the temperature constant which achieved accurate results and suggests that the choice of voltage and wire lengths was made successfully. However, some slight inaccuracies did occur in the experiment and this led to a line of ‘best-fit’ i. e. there was not a straight-line joining all of the points together being drawn.
The inaccuracies it seem could have been attributed by the following: > Inaccurately judging the wire length, the length of wire may have been slightly inaccurately judged because judging the wire to be completely straight and taut using just our eyes was extremely difficult. > Temperature change – this variable was the most difficult to keep constant and it seems that this variable was, in fact, not kept constant. It seems that the wire will heat up as soon as the power is switched on and current is allowed to flow because, as soon as the electrons start colliding with the ions in the wire, the wire gains internal energy.
Thus, it seems that, as soon as the power was switched on, the wire began to heat up, however slightly. Thus, whilst the temperature rise was kept as negligible as possible by leaving the power switched on for the minimum possible time, it seems that the temperature would have risen and this factor may have affected the results. > Meters, the ammeter and voltmeter used measured the current and volt across the wire to the degree of one hundredth of an amp and volt, respectively i. e. the current and voltage measurements may be inaccurate by the degree of up to, one hundredth of an amp/volt.
Similarly the resistance values calculated from the current and voltage measurements may be slightly inaccurate. > Contact with crocodile clips, this factor may have affected the accuracy of the results, but this is extremely unlikely as it was ensured that the crocodile clips made definite contact with the wire being used as a resistor. These factors may have produced extremely slight inaccuracies and the results were only slight inaccurate and so it seems that the minor inaccuracies that the above factors may have caused may have caused the results in the investigation to be slightly inaccurate.
Further work in the experiment could be to find the resistance of the Constantan wire used in the experiment. To find the resistance of the wire we need the two equations below, which were found from extra research. The equations tell us that the resistance of a wire is: i) Directly proportional to its length (L) i. e. R ? L ii) Inversely proportional to its cross-section area (A) i. e. R ? 1/A Combining the two statements we get: R ? L x 1/A The above can then be written as an equation if we insert a constant: Therefore, R = x L/A.
Where ‘x’ is a constant called the resistance of the material (for a fixed temperature and other physical conditions). “The resistance of a material is numerically the resistance of a sample of unit length and unit cross-section area, at a certain temperature. ” To find ‘x’ we can rearrange the equation “R = x L/A” to get “x = AR/L”. Thus, to find the resistance (x) of the Constantan wire used in this experiment we must substitute for A, R and L in the equation x = AR/L. > The wire being used in the investigation should have a uniform cross-sectional area, but, to confirm this, the diameter of the wire can be measured using a micrometer.
In this investigation the diameter of the wire was 0. 02mm and so the cross-sectional area of the wire can be estimated, by assuming the wire’s cross-section is circular, using the equation: Cross-sectional area = ? r2 Where ‘r’ is the radius of the circular cross-sectional area, which is half of the diameter ; Other ways to further the experiment would be to use wires made from different materials to find differences in resistance that each wire produced. It could then be decided which of the wires was the best conductor.
Cross-sectional area could also be investigated, if the experiment was furthered, and it could be investigated whether the resistance of a wire is inversely proportional to its cross-sectional area. To investigate the effect of cross-sectional area on resistance of similar wires (i. e. wires of the same length, material, etc. ) with different cross-sectional areas will be used. ; The effect of temperature on a wire could also be investigated. I believe that the experiment was performed successfully and that the results obtained were accurate.
The predictions that were made were also confirmed by the results and the wire obeyed the rules that it was expected to. This experiment we can confirm that the resistance of a wire is directly proportional to the wire’s length. Tarique Sabah Physics Coursework Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.