Detailed method: - I set up the circuit as shown in the diagram that I have drawn. I started the experiment by taping a meter ruler between the terminal blocks P, Q so that I could measure 100 cm of nichrome wire. I made sure that the wire was carefully tightened at both terminals to try to minimise the kinks or twists in the wire. I then switched on the power pack supply and adjusted the variable resistor until a constant current of 0. 2 A was flowing through the circuit. I then recorded the corresponding voltage reading that was displayed on the digital voltmeter.
I repeated this procedure using different lengths ranging from 30-100 cm and adjusting the variable resistor until 0. 2 A was flowing through the circuit. After recording the corresponding voltage readings for each length and tabulating them I decided to repeat the whole experiment again another 2 times so that I could take the average voltmeter reading for each length. Using a micrometer screw-gauge I measured the diameter of the wire at 3 different positions along the wire and then calculated its average diameter from the 3 values. I then plotted a graph of the length of the wire against average resistance and used it to calculate the resistivity of nichrome as mentioned in my plan where the average resistance can be calculated using the relation? ? ? R = ? ? V. I Variables in the experiment: - In this experiment I varied the length of the wire each time using a range of lengths from 30-100 cm.
I kept the current flowing through the circuit constant using a variable resistor which I kept varying for each length of wire so that the ammeter would always read 0. 2 A. I then recorded the voltage readings from the voltmeter which corresponded to the length of the wire being used. The temperature of the wires in the circuit needed to be kept constant to prevent the whole circuit from overheating. I managed to do this by quickly switching off the power pack supply every time I had recorded my set of readings. I then left the power pack to rest for a small interval of time before switching it on again to record the next set of readings.
I also kept the diameter of the wire constant by using the same piece of wire throughout the whole experiment. Factors 1. Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons.
This increase in collisions means that there will be an increase in resistance. 2. Material: The type of material will affect the amount of free electrons which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available.
If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase. 3. Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase. 4.
Wire width: If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.