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Investigating Resistance

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Kelly Waites Investigating Resistance Aim To find out the factors that affect the resistance of a wire. Also to find out the relationship between resistance and length, and resistance and cross-sectional area. Theory The current flowing through a metal wire is proportional to the potential difference across it providing the temperature of the wire remains constant. Resistance (R) = Pd across the wire (V) Current through the wire (I) If a conductor obeys ohm's law, the current will increase in proportion to the potential difference. If you double the voltage, the current will also double. If the graph of the current against potential difference is not a straight line, or does not pass through zero, then ohm's law does not apply. The amount of resistance of a wire depends on many different factors. Some of these factors are: . Length . Thickness . Material type . Temperature Resistance is the opposition to a flow of electric current in a wire. Longer wires have more resistance than shorter wires, this is because there are more particles for the electrons to get passed from one end of the wire to the other because there is a greater distance to travel. Energy is lost each time the electron hits an atom. The friction that occurs between the electrons colliding into each other as well as the atoms in the metal creates heat and heat is a major factor that effects the resistance of a wire. The heat increases, the particles that make up the wire vibrate more, which means the electrons lose more energy. ...read more.


The wire used was nichrome-24swg. LENGTH (CM) V VOLTS I AMPS R RESISTANCE V2 I2 R2 V3 I3 R3 100 4.78 1.10 4.34 5.00 1.15 4.34 5.02 1.16 4.32 80 4.53 1.31 3.45 4.55 1.27 3.58 4.77 1.39 3.43 60 4.30 1.67 2.69 4.22 1.58 2.67 4.39 1.76 3.48 40 3.86 2.16 1.78 3.70 2.07 1.77 3.81 2.39 1.59 20 2.85 3.25 0.87 2.85 2.85 0.07 3.07 3.23 0.94 The results do prove my prediction correct but to show it accurately I will change my plan of action to going down in 10cm rather than 20cm. This will give me a wider range of results. Improved Plan of Action I am going to find out what affects the resistance of a wire by using a six volt power supply, five different thickness' of nichrome wire and the changing of length from 100cm, down every 10 until I get to 10cm. The thickness' that I will use are 20, 24, 28, 32 and 36swg. For each thickness I will record the Volts and Amps from 100cm down to 10cm. I will do this by setting up a circuit like the one below and changing the wire after I have recorded all the results for the previous wire: I will the use the results to find the resistance for each length of each wire using this equation: R=V which is .... Resistance = Volts R Amps I will then do the same as the above but only record all the wires at 50cm three times to compare cross-sectional area and resistance. Then I'll do the graphs. ...read more.


The graph comparing cross-sectional area with resistance shows that with each increase in width of a uniform nature, the resistance drops, but by a greater amount each time, i.e. 32swg-10 28swg-5 diff-5 24swg-2 diff-2 20swg-0.9 diff-1.6 If I was to do the experiment again then I would improve my method by being more accurate with my measurements of the wire. The problem with the measurements before was that the wires were very bendy and hard to straighten out so as a result the wires would have been longer then the actual length recorded, so I would use straight wire and would make sure it was cut to the nearest mm to get more accurate results. Overall I am quite pleased with my experiment. The results were generally successful and prove my prediction and the theory correct. If I could do it again then I would make sure I had all the correct wires for each experiment, and that the wires weren't too hot as to affect the results in a major way by creating too much resistance. I would do this by leaving a longer period of cooling time so the heat will escape and the resistance will drop. There was two anomalous results on the graph comparing length and resistance. The reasons for these could have been an accumulation of not holding the crocodile clips at the right places, e.g. At 50cm instead of 60cm, or the connections that sent the current through the wire may have been held on tighter on one of the distances resulting in a stronger current and less resistance, and loser on the next resulting in a lower current and more resistance. ...read more.

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