For my investigation I wired several different wire all with different properties and width of wire to collect results for different resistance in wires. The three different types of wire I used were Constantan 28 wire Constantane32 and copper wire 28. Each wire was subjected to 2 volts at various different lengths of the wire. I measured the voltage and amperes every 10-center meter down a meter long length of wire. 28 Constantan wires are o. 40mm in diameter and Constantan 32 was 0. 28mm in diameter, which is 1/4 smaller then 28 I got this information from a secondary source Philip Harris Catalog.
I turn I wired up each wire as 100cm subjected it to two volts then measured the amperes and voltage. The results I’ve obtained show slight internal resistance as the current increases but this difference we assume is negligible we can safely ignore this factor. Once the results were obtained I found out the resistance of each wire via voltage divided by amperes. The safety aspect of the investigation I keep the voltage to a minimum of two amps and when of the shorter lengths of wire keep it live for shortest time possible to avoid the wire heating up.
The accuracy of human error and visual gauges is limited the voltage is limited to 0. 02 were the ampere meter is limited to 0. 2. Prediction From a secondary source Roger Muncaster a-level physics textbook author state ohms law. The Constantan wire 28 and 32 both obey Ohm’s law was if you double the length of the wire the resistance would also double. It will not be exact but this is down to some internal resistance on a Constantan 32 section of wire 50cm of wire has a resistance of 6. 30 and 100cm of wire had a resistance of 11. 50. Copper doesn’t follow Ohm’s law when the wire gets hot the resistance increases.
The copper heats up as it gets to the lower lengths of the wire. The graph of the Constantan wire will be strait line as they obey Ohm’s law but the copper doesn’t. Because of coppers properties graph will be strait, until the lower length resistances, which will be too high for their resistances and look like a few anomalies in the graph and data. Table of Results Copper 1 32 Copper 2 32 Length of wire (cm) V in volts I in amps R is ohms Length of wire (cm) V in volts I in amps R is ohms Constantan 32 1 Constantan 32 2 Length of wire (cm) V in volts I in amps R is ohms Length of wire (cm) V in volts I in amps R is ohms 1 Constantan 28 1 Constantan 28 2 Length of wire (cm) V in volts I in amps R is ohms Length of wire (cm) V in volts I in amps R is ohms Resistivity The electrical resistivity of a material is defined by R = resistance ? L = length of the conductor
A = area of the cross-section of the conductor P = the resistivity of the material of which the conductor is made This equation is for the resistivity of Constantanrom Roger Muncaster states Copper 1. 7 x 10-8 This is pleasing because my results are only 0. 3 off what roger Muncaster states.
We can prove that Ohms law works by looking at Constantan wire. 50cm = 6. 30 ohms 100cm = 11. 50 ohms This shows that Constantan wire when doubled in length will double in resistance. Evaluation My prediction that when doubling the length of the wire the resistance would double also was in the Constantan wire true, therefore we can assume it follows ohms law. The copper wire seamed to follow ohms law until we got to the shorter lengths of wire were the length of wire was sufficient to heat up and disorientate the graph, Thus from this we can see that copper doesn’t obey Ohms law.
The double the length the double resistant could be interpreted into the more wire mass the current flows in the more resistance, If this is so if you doubled the diameter you should double the resistance as well. I’m undecided whether my results would be different for the Constantan wire if we used a longer wire strip and a increased voltage we may have had a different story. 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.