Investigating The Factors Which Affect The Resistance Of A Piece Of Putty resistance Of a piece of resistance putty Planning: This investigation is designed to look into the resistance of different materials, in this case, resistance putty in the form of wires, and their conducting capability in different shapes. We must bear in mind though that different thickness and length of the putty used to make up the wire itself will affect the electric conduction capability. Therefore, the factors are; ? The thickness of the putty e.g. 1mm, 2mm, 3mm in diameter or 1 cm in diameter And also ? The length of the putty e.g.25cm, 50cm, 75cm long. The experiment will require both the readings of voltage and current in order to produce the value of resistance according to the formula; R= V/ I The current flowing through the wire will be recorded to the nearest 0.01A, using an ammeter placed in series with the circuit.
The voltage across the putty will also be measured and recorded to the nearest 0.01V, using a voltmeter placed parallel across the putty. To make it a fair test, the cell terminals will be reversed after the first readings, so that the current would flow in the opposite direction, and then be recorded down again to give repeat readings. The 2 readings for (I) or current will then be averaged, and the 2 readings for (V) or voltage will also be averaged. So that I could calculate the resistance by using the formula: R=V / I (resistance = voltage/current) or (resistance potential difference across the wire/current through the wire) The putty will be 20cm long. Making sure that this is a fair test and experiment, the putty will have a diameter of a one-penny coin at all times.
We use the one penny coin, because it will keep the putty even, and so that the crocodile clips which will be placed at each end of the putty wont squash the ends of the putty. The experiment will be repeated 10 times altogether, shorting the wire 2cm each time, to give a range of 20cm to 2cm. Safety precautions: ? Make sure that the circuit is properly connected before turning the power supply on, and do not touch the apparatus, especially the tested wire, in case the putty, until the power is switched off. ? The changing of the putty should only occur when the power is off. ? Do not carry out the experiment in wet areas, as water is a very good conductor.
? Do not switch on the power pack when there is no resistant wire (putty) and do not turn the power supply up too high, because normal laboratory wires may melt, and so might the putty. ? Do not handle experiment with wet hands. ? Place asbestos mat underneath putty for safety. ? Place a variable resistor in the circuit for safety to ensure that the current did not remain too large, but remained set at the same value throughout the experiment to ensure that the test was fair. Prediction: The factor I am investigating for this experiment is the length.
The length will change throughout the experiment but not the area. I predict that when the length of the putty increases, so wills the resistance. I also think that the length of the putty will be directly proportional to the resistance of the putty, which means that there will be a direct relationship. So, overall, when the length of the putty gets bigger the resistance will get bigger too. Theory: I chose my prediction because; longer wires will cause an increase in resistance, because the electrons have to travel past more atoms and collisions than they do in shorter wires, in this case the putty.
This means that it will take a longer time for electrons to past through a long piece of putty than a short piece of putty, and that is why there will be a big value in resistance. (The longer the putty the bigger the resistance). Also, long thin putty has more resistance than a short thick one of the same material. Also, Ohms law states that for a wire under constant physical conditions, the current is proportional to the voltage. This is also equivalent to stating that resistance is constant. If the current through a conductor is I when the voltage across it is V, its resistance R is defined by R= V / I.
Resistance (R) is measured in Ohms (?). The ohm is the resistance of a conductor in which the current is 1 ampere when a voltage of 1 volt is applied across it. Metals and some alloys give I-V graphs, which are a straight line through the origin, so long as their resistance is constant. Current (I) is directly proportional to Voltage (V) for example, I V. Doubling V doubles I etc. Such conductors obey Ohms Law, stated as follows: The current through a metallic conductor is directly proportional to the voltage across its ends if the temperature and other conditions are constant.
These are called ohmic or liner conductors and since I V, it follows that V / I = constant. The resistance of an ohmic conductor therefore does not change when the voltage does. Method: Diagram: The equipment needed consists of: Key: ? Ordinary wires Switch putty ? A power pack ? Ammeter variable resistor ammeter ? Voltmeter ? 2 crocodile clips battery cell ? putty ? 2 one penny coins voltmeter ? variable resistor The apparatus was set up as shown on the diagram. 20cm of putty was fixed between P and Q, with a one-penny coin at both ends, using crocodile clips. An asbestos mat was placed underneath the wire for safety.
The current flowing through the wire was recorded to the nearest 0.01A using an ammeter placed in series, in the circuit. The voltage across the wire was measured to the nearest 0.01V using a voltmeter placed in parallel, across the wire. The cell terminals were then reserved so that the current would flow in the opposite direction and the readings of V and I, were again taken, then recorded to give repeat readings. The 2 readings for current or I were averaged, and the 2 readings for V or voltage were averaged. The resistance was the calculated using the formula; R=V / I The length of the putty was recorded.
The putty was 20cm to start off with, and 2cm were then cut off after each reading. The experiment was repeated 10 times. Each time 2cm was cut off, the current through the wire and the voltage across the wire changed. The new readings of the current and voltage were taken, repeated the averaged as before, and R was calculated. As mentioned before, the experiment was repeated 10 times altogether, shorting the wire 2cm each time, to give a range of 20cm to 2cm.