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The factors affecting the resistance of a metalic conductor.

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INVESTIGATION: THE FACTORS AFFECTING THE RESISTANCE OF A METALLIC CONDUCTOR Metals conduct electricity because the electrons in the metal can move about inside the structure. These electrons are called free electrons. Electricity is conducted through a conductor by means of free electrons. Atoms consist of protons, electrons and neutrons. The protons and neutrons make the nucleus of an atom while the electrons circle the outer area of the atom. Electrons in metal are able to move freely and are used as current in an electric circuit. This is because they carry a charge and can move all around the circuit with this charge. While these electrons are travelling around the circuit, atoms are sometimes in the way, causing the two to collide. This takes out some of the energy from the electron and transfers it to the atom. This is how resistance occurs. The number of free electrons depends on the material and the more the free electrons in a substance the better the material as a conductor. All conductors offer resistance to the flow of current. The conductor's atoms determine this resistance. For example copper atoms offer negligible resistance to an electric current because a significant proportion of its electrons are free to move from electron to electron. Thus copper is commonly used as a conductor. Current, is the flow of electrons around a circuit. Those materials, which have a lot of "free" electrons, will make it a lot easier for current to flow through, and so there is low resistance. That's why not all metals are equally as good at conducting electricity. Therefore materials with a low resistance are called good conductors and those with a high resistance are called good insulators. In many materials there is a simple relationship between the voltage across two points and the resulting current. Such materials are called ohmic materials and obey what is known as ohms law, which sates that: "The current through a metallic conductor at a constant temperature is proportional to the potential difference (voltage)" ...read more.


* I then did the same for the cross sectional area readings of the wire and used wires that were 0.4mm, 0.56mm, 0.71mm and 0.91mm thick as compared to using wires of 0.6mm and 0.8mm. * I then set up the experiment to find out how the material affected the resistance of the wire. Below are the results of my testing in tabular and graphical form: RESULTS FOR TESTING FACTORS AFFECTING THE RESISTANCE OF A WIRE: 1. Length: Thickness of wire is 0.4mm Material is nichrome Length = 50cm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 R = 5.06 Length = 100cm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 R = 9.83 Length = 150 cm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 R = 14.63 Length = 200cm: Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 R = 19.87 2. Cross-sectional area Length of wire is 100cm Material is nichrome Thickness = 0.4mm: Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 Thickness = 0.56mm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 Thickness = 0.71mm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 Thickness = 0.91mm Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 4. Type of circuit: Length = 20' cm 30'cm Thickness = 0.4mm Series circuit: Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 Length = 100cm Thickness= 0.4mm Parallel circuit: Sr. no Voltage [v] Current [Amps] Current [amps] R = V/I I1 12 As I have found from my experiments, the results I obtained show that the factors I predicted of affecting the resistance of a wire have proved true. Firstly, the factor of length increasing and resulting in an increase of resistance of the wire held true, because, as I varied the lengths of the wire form 50cm to 200cm the resistance increased from approximately 5 to 20. ...read more.


As the graph shows, almost no current flows if the voltage applied is in the reverse direction. Testing the transistor: Testing a unijunction transistor (UJT) is a relatively easy task if you view the UJT as being a diode connected to the junction of two resistors, as shown in figure 4-21. With an ohmmeter, measure the resistance between base 1 and base 2; then reverse the ohmmeter leads and take another reading. Both readings should show the same high resistance regardless of the meter lead polarity. Connect the ohmmeter's negative lead to the UJT's emitter. Using the positive lead, measure the resistance from the emitter to base 1, and then from the emitter to base 2. Both readings should indicate high resistances approximately equal to each other. Disconnect the negative lead from the emitter and connect the positive lead to it. Using the negative lead, measure the resistance from the emitter to base. From my mathematical deductions (to further prove my investigation) in my analysis section I calculated the value for resistivity for a nichrome wire and compared the calculated value with the actual standard value of rho. That is; LENGTH [cm] R from my experimental results R from my graphical results. R/L [/cm] 50 5.06 5 0.10 100 9.83 10 0.099 150 14.63 13 0.092 200 19.87 20 0.099 AREA [m] R from my experimental results [] R from my graphical results [] R X A [m ] 1.26 x 10 5.49 4.8 6.47 2.5 x 10 2.86 3 7.32 3.96 x 10 1.62 1.8 6.77 6.5 x 10 0.97 0.9 6.04 = RA/L therefore; Material Length [m] Area [m ] Resistance [] Calculated [m] Standard [m] Nichrome 1.50 1.26 x 10 13.81 116.0 x 10 110 x 10 Nichrome Nichrome Nichrome Thus we see that my results were not so different from the actual standard value of resistivity, and this is mainly because of the temperature variations that occurred during my experiment. This evidence does support a firm conclusion that if someone was to repeat the same investigation I would expect the to receive the same results. ...read more.

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4 star(s)

This is a report that contains a lot of detail.
1. There are several subheadings missing from the report.
2. The tables of results need to be filled in.
3. Some of the information is in the wrong section.

Marked by teacher Luke Smithen 13/08/2013

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