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GCSE: Electricity and Magnetism
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From the results that I got in my preliminary experiment I have decided to measure the resistance going up 10 every time. Length(cm) 10 20 30 40 50 60 Resistance(ohms) 0.7 1.1 1.6 2.0 2.4 2.9 I have decided to use 0.8 as my current as this worked best with my wire in my preliminary experiment. It also means that my maximum voltage is low enough not to overheat the wire and cause any injury. My variable is going to be length, I decided to use this, as it is easiest to measure and seems to have a significant effect on the resistance as you can tell from the results from my preliminary experiment.
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wire, or: RESISTANCE = K/AREA OF CROSS SECTION OR RESISTANCE 1/AREA OF CROSS SECTION Length of the wire A theory along the same line of this applies to the length of the wire. As described above, in a wire, the ions cause resistance by colliding into each other. When the length of a wire is increased, there are many more ions to collide into each other. Therefore, the chance of ions colliding is increased, and the resistance is increased. When a circuit is increased in length, it is much more of a struggle for electrons to go round, because there are more obstacles, there are many more wire particles (acting like obstacles)
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Additionally, I will check that the wire material is always the same. Furthermore, I will be keeping the power supply at 6 Volts exactly. Reliability- To make sure I achieve the most reliable and accurate readings from the amp and voltmeters, I will always repeat each wire three time- therefore getting the most reliable result possible. Accuracy- I will make sure I will get extremely accurate results by having one person in my group taking the ammeter reading, and another person taking the voltmeter reading, therefore getting the most accurate findings. I will take these readings three times, and find the average result. I will also round my findings to nearest number.
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The aim of the experiment 'resistance of a wire' is to find out whether certain variables affect the resistance of a wire. These are length of a wire, thickness, material, and temperature of the wire.
Higher resistance is proven from thicker, longer wires and resistance also varies with temperature. Some metals with lower temperatures have zero resistance. When a wire has five centimetre length it will be double one with a two and a half centimetre length, and the same applies to thickness. Different types of wire have many different properties and therefore different wires have different resistances. Other things that effect resistance are called variables. Variables alter the results as they change factors around the experiment. Hypothesis: I predict that the longer the wire, the higher the resistance and the same is applicable to thickness and temperature.
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Because of this increased space between the atoms, there should be fewer collisions. If the cross-sectional area of the wire were greater, the resistance would be less because more current will be able to flow through the wire. Temperature: If the wire is heated up, the atoms in the wire will start to vibrate more rapidly. This will cause more collisions between the electrons and the atoms, due to atoms moving into the path of the flowing electrons. This increase in collisions means that there will be an increase in resistance. Wire density: If the wire has a higher density, the resistance will be higher.
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The topic of which I have been studying is energy transfers, how energy can not be destroyed but only changed into another such as potential into kinetic, this the energy transfer which shall take place in my investigation.
First I will mark a meter on the bench from where I will hold the ramp. After I have measured the 0.20 meters height I will roll the bouncy ball down the ramp and time it once it has reach the foot of the ramp and stop the stopwatch once the ball has reached the meter mark. I will do this three times so that my results are accurate and then find my average of the three. After doing the 0.20 meters three times I will raise the ramp another 0.20 meters and continue what I have done.
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I will be studying the resistance of wire, to gain a better understanding of resistance and connecting topics.
Temperature is one of the most important factors that affect resistance. Ohm's law states that if all the factors that affect resistance in a wire remain constant, THEN the current is directly proportional to the p.d. across it. Resistance is responsible for the current that flows - high resistance produces a low current and low resistance a high current. Resistance is often evident as the conversion of electrical energy to heat. I might expect the wire to get hot to show that there is resistance. RESISTIVITY is a property of a conductor that tells you how hard it is to push current through it.
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I will do each of these experiments 3 time, I will also take readings for each length from 100cm to 10cm also taking the reading of each 10cm in-between e.g. 100cm, 90cm, 80cm and so forth. Each time I change the length of the wire I must alternate the variable resistor to assure the current is the same reading each time. Equipment list: * Power pack * 105cm of constantan wire (extra 5cm for placement of crocodile clips) * connecting wires * Variable resistors * Ammeter * Voltmeter * Meter stick * Crocodile clips Safety To make this experiment safe I must be aware of the electrical current that will be around me.
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The voltmeter is set on 20 volts because we are measuring volts and it gives us a wide range results. Apparatus The apparatus we will be using in this experiment are: Procedure 1. The procedure of the experiment is to set up the apparatus in the diagram above. 2. Next is to measure the length of wire you are going to use for the experiment. Either 10cm, 20cm30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm, 100cm with a range of 0 to 100cm.
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10.5 1.625 6.46 11.0 1.65 11.0 1.65 11.0 1.65 6.67 Analysis After conducting my experiment and analysing my results I have found that a light bulb does not obey ohm's law, it is a non-ohmic conductor. From the graph obtained from the results it is clearly shown how ohm's law doesn't apply to the light bulb. The graph clearly shows that the current is not proportional to the voltage. The graph shows that as the voltage increased the increase in current was reduced.
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Move the crocodile clip another 5 cm along. 8. Repeat steps 2-6. 9. Move the crocodile clip another 5 cm along the wire. 10. Repeat steps 2-6. 11. Move the crocodile clip another 5 cm along the wire. 12. Repeat 2-6. 13. Move the crocodile clip another 5 cm along the wire. 14. Repeat steps 2-6. 15. Calculate the resistance for each length. To investigate the variable length follow this method: 1.Place one crocodile clip at one end and fold the wire 20 cm along and clip the next crocodile clip.(SGW - 28) 2. Place in tub of water.
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The effect is described by Joule's law. The equation for resistance is R=V/I; ?=V/A; resistance= voltage (p.d.)/current. IV graphs compare the current to the voltage of various conductors. Here are 4 main IV graphs. Resistor, the current is proportional to the voltage. Wires, different wires have different resistances hence the different slopes. Filament bulb, as the temperature of the filament increases, the resistance increases hence the curve. Diode, the current will only flow in one direction as shown. Electrical conduction is the flow of electric current through matter.
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So he came up with this equation: Resistance, R = p.d across the wire (v) Current through the wire (I) From this information he came up with this graph: This graph is an ideal ohmic conductor. An ohmic conductor is a graph that follows Ohm's law. First I am going to look at the effect of changing the length of the wire. Inside a wire there are atoms and when a current is pushed through it the electrons from the current pass from one atom to another. Electrons need to use more energy if there are more atoms inside the wire because there is more work for the electrons to do.
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Thus causing higher resistance. The resistance and the length should be directly proportional to each other therefore. In a long piece of wire there are more atoms so there is less room for the electrons to get through. The electrons bump into the atoms and lose some of their energy. However in a short piece of wire, there are fewer atoms. This means that it is easier for the electrons to move through the wire. Apparatus We used the following apparatus: _ A meter rule, 30 Nichrome wire, seven other wires, a variable resistor, a 6 volt battery and two crocodile clips.
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amount then record the volts and amps of that circuit then repeat this step again so I have three sets of results * I will repeat the last four steps for these lengths of wire. 500mm, 400mm, 300mm, 200mm and 100mm. * I will then record my results in neat and work out the resistance for each set of results (totalling 18 sets of voltage and current) by using the R=V�I formula * Then, using the resistance I worked out, I will find the average resistance for each length of wire The Science In every circuit there is always resistance.
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bending may also affect the resistance in the wire. Measurements should be taken at regular intervals of 10cm, starting with 10 cm and ending with 100cm. It will be taken as accurately as possible ( to 1 dp if necessary) so that a reliable set of results are produced. The length should be precisely from the inside edges of the crocodile clips. Eg Every 10cm, current and voltage values must be written down so that resistance can be worked out by VOLTAGE/CURRENT.
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See if there is a relationship between resistance and length for Nickel-chrome wire of a diameter 0.19mm.
The current should stay constant the whole time. By changing only 1 variable, the length of wire, I aim to keep this test fair. All other variables such as voltage , type of wire, diameter of wire and the accuracy of my apparatus will all be kept constant throughout the experiment. One possible source of error is due to a temperature rise due to current passing through the wire over a long period of time. This heat will increase the error in my data because the heat will increase the resistance of the wire.
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down the wire. Turn the power pack on at 3v and record measurements from the voltmeter and ammeter. Repeat this with 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm, and 1m of wire, and record the reading for amps and volts for each length of wire. Do each length 3 times, to give 3 independent sets of results. The reason for repeating the experiment is to make sure none of the results are wrong or seem out of place, and to make sure no mistakes are made in setting up the experiment.
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For each length of wire I will record the Voltage and current flowing through the circuit. I will repeat these results twice, so that I can get the average. I will calculate the resistance from these results. From this I will be able to see the relationship between the length of wire and the resistance. It will be a fair test, as I will only change the length of wire and none of the other variables mentioned below. I will always have 2V flowing through the circuit. The length of wire will increase by 5cm each time, I will start with 5cm long, and the length will increase.
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I will also use a small current, which will help to keep the temperature down. I will be varying the length of the wire to investigate the change in resistance at different lengths of wire. I will be using the apparatus as is shown in the diagram above. The ammeter and voltmeter will be set to an appropriate scale. The protection resistor is used to prevent short-circuiting and over-heating. I am going to measure the length of the wire to the nearest mm measured between the crocodile clips.
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Thickness of wire decreases the resistance, as there is more room for the electrons to travel past the atoms. They don't collide as much. Length of wire increases the resistance because the electrons have further to move and more collisions occur. So, if you double the length of wire, you double the resistance. Because the number of atoms and the number of collisions doubles. Type of wire affects resistance because different types have different atom arrangements. Some have different patterns, and some are arranged so that electrons have an easier path to travel through the atoms. Fair Test. To make the experiment fair, I will make sure that the temperature stays the same flowing through the power pack and wire.
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I will refrain from changing the number of cells used so that the maximum voltage is kept constant and this will not affect the resistance. I will plot a graph showing average resistance against length. This will show whether the average resistance and the length of the wires are directly proportional. I measured the resistances of nichrome 1 (diameter 0.274mm), nichrome 2 (diameter 0.457mm), and copper (diameter 0.274mm) wires at lengths of 40 cm and 100 cm and currents of 20 mA and 100 mA to help me decide which of the three wires I would use.
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A technician has the problem of making wire resistors of various values. Plan and carry out an investigation to help the technician solve the problem.
Predictions I predict that has I increase the length of wire, the resistance will also increase. The length of a wire affects its resistance to the flow of the charges through the wire. This determines how much current (i.e. flow of charge i.e. electrons) flows in the wire. Types of variables Independent This is the length of wire we will use in the circuit in which the current will flow and the voltage. Dependant This is what we measure; this will be the current and resistance. Control This is what is kept the same. This will be the other variables: temperature, cross section area of wire and material.
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The aim of this experiment to find the relationship between length of wire and the resistance it will create.
Why can metals conduct electricity: Metal atoms have outer electrons which are not tied to any one atom. These electrons can move freely within the structure of a metal. When more electrons are pushed into a piece of metal (by an electric current for example) the electrons just flow through the metal in between the metal atoms. The electric current flowing through the wire is a flow of electrons. Electrons have a negative charge. There are no such free electrons in covalent or ionic solids, so electrons can't flow through them - they are non-conductors. Aim: The aim of this experiment to find the relationship between length of wire and the resistance it will create.
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In this investigation I will be looking at how the resistance of the wire changes when I change a factor and keep the rest constant.
Resistivity is expressed in terms of the ohms resistance per cubic centimetre of the substance at 20�C (68�F). The term resistance is also used when the flow of a fluid or heat is impeded. The forces of friction provide the resistance to the flow of a fluid in a pipe, and insulation provides thermal resistance that reduces the flow of heat from a higher to a lower temperature. Bibliography I gathered this information from Microsoft Encarta '95 and The Dorling Kindersley.
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