Planning section During this experiment, I shall begin with a preliminary investigation in order to aid my final practical to be as accurate as humanely possible. Preliminary experiment Apparatus In this investigation I shall need: o A piece of constantan wire, longer than 100 cm o Two ammeters, both analogue and digital o Two voltmeters, both analogue and digital o A power pack o A 100 cm ruler Diagram Method The apparatus was set up as shown in the diagram. Although in this investigation’s preliminary experiment I shall not be taking results, I shall be entertaining the ideas of ways to improve the experiment.
I shall set up the circuit as shown in the diagram, and I shall be investigating: 1 – If Analogue or digital meters are better 2 – Which voltage to use 3 – Which lengths to collect results from Evaluation During this experiment, as afore mentioned in the method, I explored what was the best possible way of conducting the final experiment? I have included in this section which methods of experimentation I shall be using in the final practical; Digital or analogue The reason that during the practical investigation I used both digital and analogue meters was to establish which of the two would be best suited to my particular investigations.
During the practical I observed several key problems and several benefits of both. Analogue meters did not ‘flicker’ between two readings, but as they were not digital made it subsequently difficult to read accurately to two decimal places – a problem which the digital meters did not have. The digital meters although they had difficulties with ‘flickering’ they tended to rest on a specific value for the majority of the readings, and as they measured accurately to two decimal places, I dubbed them the best of the two varieties of meter.
Measuring method During the experiment, I believe it best to use two values – namely voltage and current – to find the value for resistance easily. These will be taken by using a digital ammeter placed in series in the circuit. I will also use a digital voltmeter, placed in parallel in the circuit. Affecting factors The resistance is affected by several major factors. These are: Temperature of wire Cross-sectional area of wire Length of wire Voltage and current of the circuit Circuit type
The circuit type that I have chosen for this practical will be a series circuit as in a parallel circuit, the current and voltage of the circuit is dissipated throughout the different components on the circuit. Also I have chosen series, as there is only one key component in the circuit, which is the contra wire as the other components are either meters or precautionary measures. Fair testing To ensure that the experiment is a fair test, several conditions must be kept constant, the most obvious of those is the wire itself.
I have measured the wire with a set of callipers and found it to be of consistent cross sectional area. This area is 0. 36mm across and therefore the wire is constant. The wire must be close to the same temperature. The reason that I have stated close to the same temperature is that resistance due to temperature change is only during extreme cases – in as much that super conductors must be kept frozen in liquid nitrogen in order for them to be effective, so the readings wouldn’t be too far out if the wire is a couple of degrees warmer or cooler than that of the original reading.
I will attempt to ensure close to the same temperature by turning the power off whilst I am not taking readings, also I shall not use a voltage higher than 6v as this causes the wire to melt easily – a consequence learnt in the preliminary. I have also researched temperature increases in wires on the internet, and wires do quickly rise in temperature, especially something as fragile as constantan wire. This principle is in use in fuses. The length of wire must be kept constant between sets of readings. This will be done by strapping the wire to a ruler using a non-conductor, i. e. Selotape.
Also I will be precise in the positioning of my crocodile clips whilst changing wire length. Sets of readings During the final practical I shall take two sets of readings from three various voltages. I shall take two sets of each as one or more results could be anomalous, and also to ensure that my experiment is more accurate. I shall take the readings from 2v, 4v and 6v, I shall not conduct experiments in any more than 6v as the wire then begins to melt due to the increased flow of electrons in the wire, causing the metal particles to gain more and more energy – as thermal energy – eventually to cause an undesired melting effect of the wire.
The physics behind the experiment Whilst current is flowing in a circuit, free electrons in the conducting substances are vibrating electronic energy around the circuit. This energy is called potential energy or PE for short. The electrons are given PE in the power source, and it is then used to ‘power’ the components of the circuit by effectively ‘offloading’ a certain amount of energy at each individual item. The force of resistance is counteracting the flow of free electrons by acting as a buffer to these free-moving charge carriers, and therefore the more resistance there is, the less voltage and current there is in the circuit overall.