This investigation will be to determine the relationship between the length of a conductor and its resistance. The aim is to test a number of different lengths of nichrome wire to measure the resistance of each length. To ensure a safe procedure, a low voltage battery of 12 volts will be used, and the samples to be tested will be located on an insulating mat to prevent any shorts occurring. In addition a 2 Amp fuse will be placed in the circuit as a protective measure. For a fair test, all other parameters that can affect the resistance will be kept constant.
These are the sample material, the diameter of the wire, and the temperature of the wire. To keep the temperature of the wire constant, it will be necessary to keep the current flowing in it constant. This is because the power dissipated in the conductor is I2R, so an increase of current by a factor of 2 will increase the power dissipated by a factor of 4, which can seriously affect the resistance. Thus only the length of the wire will be changed, and the corresponding voltage across it to give the same test current will be varied and measured.
The resistance of the test sample will then be given by Ohm’s Law: Resistance = Voltage (Volts)( Ohm) My prediction is that the resistance of the wire will be proportional to its length, all other variables being kept constant Equipment The equipment used for this investigation consisted of: 1) 12 volt power pack with on/off switch 2) Variable resistor (rheostat) 3) A 2 amp ammeter with digital readout to 0. 001 amp accuracy 4) A 20V voltmeter with digital readout to 0. 01V accuracy 5) Crocodile clips for connection of the test sample into the circuit and the voltmeter to the connecting crocodile clips. 6) Test samples consisting of varying lengths of 24 SWG The equipment and the circuit configuration used is shown in Fig 1.
A 12-volt power pack will be connected in series with a switch, a 2-amp fuse, an Ammeter, a variable resistor and a sample test wire. A voltmeter will be connected across the test sample by crocodile clips. The test sample was connected into the circuit using crocodile clips. The voltmeter was connected across the sample into the rear of the crocodile clips. The plan will be to vary the sample length from 10 cms to 100 cms in 10 cm increments to provide a good range of results. Also to take readings of three samples for each length, and average the voltage readings to reduce possible errors.
There are four factors that will affect the resistance of a wire. These are: 1. As the length of a wire increases, the resistance of the wire also increases. A variable resistor or rheostat is used to vary the current in a circuit. As the sliding contact moves, it varies the length of wire in the circuit. 2. As the cross-sectional area of a wire increases, the resistance of the wire decreases. An analogy of this is a water pipe, if the diameter of the water pipe is small the water flowing through will. Experience high resistance to the rate of flow. However if the diameter of the water pipe is large, the water flowing.