Introduction: This experiment is to see how and if the length of a piece of wire effects resistance within a circuit. I already know that as the tempurature changes then so does the resistance and that if the wire is straight it decreases the amount of resistance opposed to when it is not straight and the resistance is increased. Electricity is a flow of charges in a circuit, a resistor is something that opposes the flow of an electrical current within the circuit.
It is the electrons colliding with the atoms in the wire that causes the resistance. As the length of the wire increases the more atoms there will be, therfore more electrons, therefore more resistance. This then causes the charged particles to be pushed around the circuit more. Resistance is meausured in Ohms from current and potential difference: R=V/I R= Resistance in Ohms I= Current in Amps V= Potential difference in Volts Prediction: I predict that as the lenght of the wire is increased then the resistance will also increase.
I think this because within the wire it is made up of positive fixed ions with the negativly charged electrons, when the wire is connected into a circuit the charged electrons flow along the wire and become the current. When the negative electrons pass the positive fixed ions they then collide and then start to vibrate. This creates heat friction and causes the electrons to start moving more slowly and stop passing through the wire quite so quickly. The resistance has taken place and the current decreases.
“When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons. When this happens electrons move an electromotive force such as voltage, and in hitting these atoms, also creates friction of the electrons and atoms. When the wire is lengthend, the journey is considerably longer and the resistance changes” – http://www. physlink. com/Education/AskExperts/ae218. cfm Equipment: Leads x 8 Wire (1 metre) Ampmeter Voltmeter Cell Bulb Meter Stick Cellotape Crocodile Cilps x 2 Preliminary Method:
I set up the circuit using only one cell, an ammeter and a voltmeter all in series. Between the ammeter and the voltmeter I placed a bulb and the component, the wire. The wire was taped to a meter stick so to make sure that all the measurments were as accurate as possible to the nearest millmeter. I attached the wire to the leads by using two crocodile clips, one at each end. I then took readings from the ammeter and the voltmeter at 1000mm, 800mm, 600mm, 400mm and 200mm. I took each reading three times then averaged them out to make sure my results were more reliable and accurate. From this I then worked out the current.
Preliminary Results: Problems: However many problems did occur with this first experiment. First of all the ammeter and voltmeter kept comming up with negative readings or none at all. The wires kept comming loose and the wire was not straight so the measurments would not of been accurate to the nearest millimeter. I then also realised that the bulb and maybe the cellotape its self was a resistor so it would of made it an unfair test as I would of then of been testing the resistance of two resistors. It also was hard to get the wire to 1000mm as it kept comming unattached to the meter stcik and the wire its self was only just over a meter.
Solutions: I found soloutions to the majoraty of my problems. I replaced the ammeter and voltmeter to see if that made a difference but it didn’t so I checked to see that I had out the correct leads into the correct places so opposites were together (positive to negative) and the same charges wern’t (not positive to positive). I did have this problem at the ammeter and once I changed I was gettin positive readings. The voltmeter however was still showing negative readings even after it was connected properly.
I then found out that “The Voltmeter must be placed in parallel around the component under test” – page 86, AQA Modular Science Early Modules, Edited by Richard Parsons. I replaced several of the wires to make sure that they were not loose, and tried as best as possible to straighten the wire. I did this using the side of a ruler running it along it. I also tested the cellotape to see if my readings changed while having it on there which they did slightly so I only taped it down on the side of the wire that wasn’t connected in the circuit to make it a fair test.