Electrical resistance

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From the graphs 1 and 2 above, it is evident that the length is directly proportional to the resistance as the trendline is linear. [KD5]From graph 1, the average gradient was found and from graph 2, the uncertainty of the average gradient was determined. The gradient can then be substituted into the equation and rearranged to find the diameter. The diameter of the experiment was found to be 0.00055m with an uncertainty of 0.00002m, where as the actual diameter is 0.000559m given by the manufacturer (Science Supplies Australia Pty, Ldt). From this, the experimental error can be calculated.

As shown above, the experimental error is 1.61%. This means that the difference between the experimental and theoretical value has a difference of 1.61%. This experimental error is less than the uncertainty. This also shows that the theoretical value lies within the uncertainty of the experimental result. Therefore, the experiment supports the relationship between the diameter, length and resistance, which is:[KD6]

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Which could be arranged to make diameter as the subject: Sufficient concordant results were found in the experiment as the value between the maximum and minimum resistance found in the trails had the greatest difference of 0.2?. This shows that the results were consistent. The method to calculating the uncertainty of the average resistance was maximum deviation. This method considers the greatest possible error in the experiment. The uncertainties were all found to which is the same as the uncertainty of the instrument. Considering that the greatest possible error found for the average resistance was the same as the instrument, the error is considered to be quite low. The uncertainty of the length of nichrome wire was found using rules from error propagation.

The method of measuring the length required that the errors must be added together, therefore increasing the error in the experiment. This error can be improved if the nichrome was set up as a straight line and using a tape measure so that the error does not build up. Evaluation: Limitations:[KD7] The effect on the experiment:How this can be improved[KD8]  Crooked nichrome wires[KD9]

The length of the opposite knobs was measured which assumes that the nichrome wire was straight. However, the nichrome wire was actually crooked. Therefore, the actual length of the nichrome wire would be greater than the measured length. From the experiment, It was found that the length is directly proportional to the resistance. Since the actual length was longer than the measured value, the value of the resistance was larger than it should have been.

This limitation can be improved by tightening the nichrome wire. By tightening the wire, it would become straighter. Nichrome wires were bent around the knobs[KD10] The nichrome wires were bent around the knobs. Thus the measured length of the nichrome wire was smaller than it should have been. As the wire was longer than the measured value, the value of the resistance was larger than it should have been. If the size or diameter of the knobs were decreased, the length of the sector where the wire wraps around it would also decrease and minimises this limitation i.e. the size of a screw driver so that the length which wraps around the knob would be insignificant. Alternatively, the nichrome wire could be measured in a straight line so that it did not have to bend around the knobs.

The varying electrical resistivity of the nichrome wire. The composition of the nichrome wire varies and also the electrical resistivity. Therefore, the median was assumed to be the electrical resistivity. The actual electricity may have been different from the assumed value which affects the calculations of determining the diameter. By finding the percent composition of the nichrome wire, the electrical resistivity may have been estimated which will improve the accuracy of the experiment instead of assuming that the value is the median.


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