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Measuring the resistance across a length of wire.

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Introduction

H/W 26/01/03 Measuring the resistance across a length of wire Aim It is to find out the resistance across a length of wire by changing the length of wire. Preliminary Experiment We will choose a 32 Nichroms wire due to its high resistance that will give bigger changes in our results. We got this result by testing the wire against the copper wire that we found to have a low resistance. We also decided to use a range of 0-100cm of wire with 10cm intervals to give a wide range of results. We will use a voltage of 2 volts with the ammeter set on 1 amp and the voltmeter set on 20 volts. The voltage is on 2 volts because it doesn't heat the wire up as quickly as 12 volts and gives us a sensible range of results. The ammeter is set on 1 amp because it gives us a sensible range of results and is better than 100mA scale and the 5A scale. ...read more.

Middle

The accuracy will be shown in our readings. Background Knowledge The resistors in a series circuit are shown because the more lamps you add the dimmer they get. The ammeter shows that the current gets less as you add more lamps. This means that the resistance of the circuit has increased. When we add resistors in series the total resistance goes up: Rtotal = R1 + R2 + R3 etc The resistance rises when electrons have too much objects to get through. One way the resistance raises is by heating which makes the wire atoms vibrate causing more of an obstacle to get through. Ohm's Law is for a given conductor at a constant temperature the current in its proportional to the applied voltage. We can write this as a formula I=V/R, we can use this formula to make calculations with all values of V for a given conductor. But we have to be careful, because the resistance might change if the conductor gets hot. ...read more.

Conclusion

On the graph it shows the best-fit line going up at a steady rate. Using the knowledge that I have learnt in class, the more atoms for the elections to pass through making the resistance bigger. Also on the graph it shows one point that was a little bit far from the best-fit line, which was the 40cm of wire. It is shown in my results as well with one of the readings being 0.88V. My conclusion fits with the prediction that I made because the graph is increasing just as I said so. My prediction was that the bigger length of wire, the resistance would be big therefore producing a lower current. If I did this experiment again I would get the crocodile clips to stop sliding by putting grips between them. I would also get a better range if I repeated it more times. Another thing I would do is keeping the wire at the same temperature by keeping it in a cool room. By Leigh Clements 10A/Sc1 ...read more.

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