# Investigating Resistance in an electrical circuit

The aim of this experiment is to investigate the resistance in an electrical circuit. There are many different ways to investigate the resistance in a wire, however to do so there must be some background research and prior knowledge of electrical circuits and the components. Through research I have learnt that George Simon Ohm was one of the forefathers of research into electrical resistance. And, thus accordingly resistance is measured in ohms (? ). Resistance is the “opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy. ” (www.

dictionary. com) To calculate the resistance of a wire, you need to multiply together the current and voltage: Resistance = Current x Voltage R = I x V The horizontal line is a divide sign. The calculation is started with whatever quantity that is looked for. “V=”, “I=” or “R=” all possible formulae based on this particular Ohms law will be attained. Another useful method is if you place your finger on the calculation you are looking for you are left with the formula you are looking for, that is.

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From this, we conclude that; Current equals Voltage divided by Resistance (I=V/R), Resistance equals Voltage divided by Current (R=V/I), and Voltage equals Current times Resistance (V=IR). This is ohm’s law. This is how Ohm’s Law would be applied into this question. Find the electrical resistance of a light bulb, which passes 4A of current when a potential difference of 240V is placed across it. R = V/I = (240V) / (4A) = 60 ? Suppose a bulb passes 3A of current when 360V is put across it, what then is its resistance? R = V/I = (360V) / (3A) = 120 ? Factors affecting the resistance of a wire Thickness affects the resistance of a wire.

The thicker the wire the lower the resistance because there is less resistance to the flow of electrons. If the length of a wire is doubled, the resistance is doubled. Another is the effect of temperature on a conductor. The higher the temperature, the higher the resistance. This is because the hotter the wire becomes the more vibrations make atoms “get in the way” of the electrons more often. The electrons then spend more time than necessary on diverted courses instead of going round the circuit on the shortest course possible. Different materials will also affect the resistance on a wire.

Copper is generally used in electrical circuits though ideally silver would be used in every circuit but it is expensive to use. Copper has a low resistance and is the most efficient after silver. Materials with high resistances have their purposes in some electrical circuits too. Nichrome (an alloy of 80% Nickel and 20% Chromium) is often used as a heating element in electrical devices. For my experiment I have decided that I will see whether the length of wire affects the resistance in a wire and I have also decided to see whether the thickness of the wire will also affect the resistance in a wire.

Prediction I predict that there will be higher resistance in wires that are longer in length because the path the electrons have to go through is longer. I also believe that as the length doubles the resistance will also double. I also believe that the thicker the wire is the less resistance will be present, this is because the thicker the wire the less the flow of the electrons is impeded. Preliminary To determine which type of wire to use we set up a preliminary experiment. The first was to determine what type of wire to use and the second was to determine at what intervals we would use to take results.

For example every 3cm or every 5 cm. In order to do this preliminary experiment we will need. 1 x Power Pack (to give varied voltage 1 x Voltmeter  1 x Ammeter  5 x wires (with crocodile clips)  varied wires The apparatus will be set up as shown below. The varied wires that we will use are silver, constantan, copper and nichrome. Results From doing the preliminary experiment we have determined that we should take readings from every 5cm. We have decided this because of the time scale that we are restricted to. The table below shows how long it took to take a reading of a wire of 100cm; at different intervals.

Intervals (centimetres) Time (mins) 1cm 19 2cm 11 3cm 9 5cm 6 This table shows that it is less time consuming and therefore it will enable us to get a better set of results. The second preliminary experiment was to determine what type of wire we should use. The three elements that I was looking at were availability, cost and safety. Nichrome: The nichrome wire was easily accessible and was not expensive. The only problem with the nichrome was that if I went to a low length it heated up quickly which created a safety issue. It is for this reason I will not use the Nichrome wire. Silver: The silver was not accessible.

We were unable to find 100cm of silver wire and it is very expensive. For these reason we will not be using silver wire. Copper: copper wire is the cheapest wire and is also the safest wire. However many other pupils are using copper wire and the availability will not be sufficient. After conferring with my classmates and my teacher I have decided not to use copper wire Constantan: constantan wire was easily accessible and it is available in many thicknesses. It is safe as long as the voltage is kept low. After doing the preliminary experiment I have decided to collect readings every 5 cm use a starting wire of 100cm and use constantan wire.