Current 1 (mA) Voltage2 (V) Current 2(mA) Measurements of diameter of wire at 20 cm intervals Point measured at (cm) Diameter measured (mm)Final data (allowing for end error) I then checked the end error of the micrometer was +0. 04mm leaving me with the final data Percentage Errors of Apparatus Micrometer.
When the diameter is put into the equation A=? (d/2)2 the diameter is squared so the error is doubled i. e. 10. 5% Conclusion Alessadnro Bizzarri I found out that my predictions were correct. The longer the piece of wire, the greater the resistance. This is due to the idea of the free moving electrons being resisted by atoms in the wire. There would be more collisions in a longer piece of wire, which explains the increased resistance. I also predicted that the relationship between the wire length and the resistance should be directly proportional because the line pass through the origin.
I finished with a straight line graph so this prediction was also correct. This is because in a wire twice the length of another wire, there would be double the number of atoms causing resistance. From my graph my gradient is equal to 41/1. 04= 39. 42? m. Gradient= 39. 42? m. By using the formula P= Gradient ? A , I can find P. A=? (d/2) 2 =?? (0. 19? 10-3/2) 2 Area =2. 8? 10-8 P=2. 8? 10-8 ? 39. 42 P=110? 10-8? m Evaluation I am relatively pleased with the results obtained. I ended up with a wide range of results and my predictions were proved correct.
I predicted that when I plotted R against l it would produce a straight line going through the origin. My results were accurate because on my graph nearly all of the points came into contact with the line of best fit or were very close. My techniques of measuring current and voltage were also good because the variation between repeat readings of voltage and current at each length is small. Length (cm) Difference in voltage (V) Difference in Current (mA).
The range of resistances between each reading is large which gives me more spread, which makes my graph more accurate. Evaluation of results The value I have calculated for resistivity is 110? 10-8 ? /m. I looked up my data laboratory book and found it to be 110? 10-8. My unrounded value for the resistivity is 110. 3? 10-8 ? /m . This is an almost identical value to that found in the book. Sources of error In this experiment I encountered many sources of error. The inconstant thickness of wire accounts for one of them.
Although I took diameter readings along the length of wire, there could still be chinks in the wire which could affect many of my results. The crocodile clips which I used also increased error slightly. The crocodile clip was in contact with an unnecessarily large section of the wire during the experiment. Because of this, I was taking voltage and current readings for a slightly inaccurate length. This is also partly due to human error because I could have placed the crocodile clip onto the exact length I wanted. My micrometer also proved to have significant source of error.
The end error of the micrometer I used was +0. 04mm. The micrometer was also found to have the greatest percentage error. Its percentage error was doubled because the diameter it was used to measure was squared . (A=? (d/2)2). Measuring the length of my wire proved quite difficult because it was hard to get an accurate reading by eye. Even though the wire was cello taped to a meter rule there was some slackness in the wire proving that there was in fact more than a meter there. I managed to avoid getting the temperature too hot and so increased accuracy and reliability. Improvements.
Many of improvements could be put in place if I was to redo this experiment. I would buy a wire, which has the same diameter all the way through. I could also find an improvement to the crocodile clips. Instead of the clips I could use a jockey key. The length of wire which I would be collecting data for would be a lot accurate as jockey key comes into contact with the wire over a small distance compared to the crocodile clips. Further work A possible source for further work is analysing the effect of the cross sectional area of the wire with resistance. Using the equation R=pl/A in the form of Y=mx+c.
Plotting R against l/A again I could predict another straight line and the resitivity would be found. This would be the same for nickel Chrome. I could also see if the equations R? l and R? l/A are true for other types of wire.
Bibliography Physics by Tom Duncan Salters Horners advanced Physics Collins advanced modular sciences 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.