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GCSE: Electricity and Magnetism
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Accurate resistors can be made from metal wires. Two different types are carbon resistors and wire-wound resistors. Wires can be made from Manganin, Constantan and Nickrome. Ohms' law: Some objects have a high resistance to the passage of electricity through them, and others have a low resistance. The resistance of any object is fixed but it is difficult to measure directly. The resistance of an object is found by measuring the current flowing through it when a known potential difference is used. Ohms' law states that the current through a metallic conductor at constant temperature is proportional to the potential difference, thus the potential difference or current is constant.
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Prediction I predict that the longer the wire the bigger the resistance. Resistance Metals are made up of atoms. Electrons move through the metal. The metals tries to stop the electrons passing through this causes resistance. When you double the length you double the resistance. Results table Length V I R V I R V I R Average 10CM 2.00 0.81 2.46 1.76 0.94 1.87 1.75 0.88 1.98 2.10 20CM 2.18 0.56 3.89 2.15 0.57 3.77 2.09 0.56 3.73 3.79 30CM 2.33 0.41 5.68 2.31 0.40 5.77 2.25 0.39 5.76 5.73 40CM 2.40 0.31 7.74 2.41 0.32 7.53 2.36 0.31 7.61 7.47 50CM 2.50 0.26 9.61 2.47 0.26 11.2 2.40 0.26 9.23
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A manufacturer of resistors uses a variety of wires to make resistors of fixed values. You are to carry out tests to investigate how he can produce resistors with different values of resistance.
This shows that different materials will give different values of resistance even if their length and cross section are the same. Variables: Variables which will affect the resistance of the wire are: Length Thickness Material Resistivity Temperature Variable to be investigated: The variable which we are going to investigate will be the length. Prediction: I think that in the experiment, when we increase the length each time, the resistance will increase. Planning experimental procedures Independent Variable: My independent variable will be the length.
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An Investigation into the relationship between the forces applied to a length of wire and its extension.
Strain involves extension and original length therefore also bringing in extension, as I required this would be the variable that I will measure. The other variables involved, original length and cross sectional area will have to be maintained as constants as these are active variables I young's modulus. This is a specific form of Hooke's law of elasticity. The units of Young's modulus in the English system are pounds per square inch, and in the metric system newtons per square metre (N/m2).
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Another sort of resistance can be likened to water flowing through a thin pipe. The water cannot flow through as fast as there is less space available to flow. The analogy most like electricity is the water passing through a filter. The water collides with the filter and is thus slowed down; not as much water can pass through as quickly. Likewise, electrons collide with the nuclei of the metal ions in the wire. This slows down the electrons in much the same way as the filter slows down water. A wire with low resistance is like water through a grille, a wire with high resistance like water through many sheets of filter paper.
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Once found we divided it by the current and used that to find the resistance in ohms. First a length of wire over a metre long is laid next to a metre rule. The positive crocodile clip is attached at 0cm. And the negative is moved up and down the wire, stopping at 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100cm. Each time reading the ammeter and voltmeter to work out resistance Prediction: I predict that lengthening the wire will increase the resistance in proportion to the length.
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I predict that as the length of the wire increases the resistance will also increase in direct proportion, as there will be more particle collisions in the longer wire. In addition the free electrons in the outer shell have to carry the charge further, which also increases the chances of collision To make the experiment a fair test we will use 2 volts throughout and include a switch in the circuit, which will enable us to control that the circuit is only on when we are taking readings.
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ALCOHOL ENERGY RELEASED (KJ/mol)) Methanol -659 Ethanol -1279 Propan-1-ol -1899 Butan-1-ol -2519 The negative values mean energy is lost from the compounds and is therefore given out as heat or light as an exothermic reaction. The graph shows that as the length of alcohol chains increases the energy released by combustion will also increase directly proportionally. This is shown by the straight line passing through the origin on the graph on page 6. This is because the longer chains have give out more energy from the bonds formed in the products than the energy that went in to break the extra carbon and 2 hydrogen bonds.
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Once the results were obtained I found out the resistance of each wire via voltage divided by amperes. The safety aspect of the investigation I keep the voltage to a minimum of two amps and when of the shorter lengths of wire keep it live for shortest time possible to avoid the wire heating up. The accuracy of human error and visual gauges is limited the voltage is limited to 0.02 were the ampere meter is limited to 0.2. Prediction From a secondary source Roger Muncaster a-level physics textbook author state ohms law.
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3 X 497 = 1491 Total Energy in = 4812 kJ Total Energy out = 5472 kJ Energy Released = 4812 - 5472 = -660 kJ When a bond breaks, energy is taken in so that it has enough energy to break the bond. Also when bonds are formed, energy is given out in an exothermic reaction. Overall, more energy is given out than is taken in so the reaction as a whole is an exothermic reaction. The total energy given out is the figure at the end.
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Instead the temperature of the ice rises until it reaches zero degrees Celsius whereupon it begins to melt. During the entire melting process the contents of the bucket remain at zero degrees, however the room temperature would drop indicating that it was putting heat energy into the melting process. This heat energy is described as latent heat. Specific heat The specific heat capacity of a solid or liquid is defined as the heat required to raise unit mass of substance by one degree of temperature. Some substances have more resistance to temperature change than others so more energy is required to alter the temperature.
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* Temperature - For metal conductors, resistance increases with temperature. For semi-conductors, its decreases with temperature. I am going to investigate how length affects the resistance of a wire. I will change the length of the wire through a range of readings. My prediction is that as the wire gets shorter the resistance become smaller e.g. if it is half the length it should have half the resistance. I think this because the wire is full of atoms and the electrons have to try and get through it. So if the wire is short there is less atoms so the electrons will travel easier.
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Cross-sectional area of wire ==> The formula R = �I shows us that the cross-sectional area affects resistance. A This will be done again by using the same wire throughout the experiment. Prediction I predict that the resistance of the wire will be directly proportional to the length. Atoms in the material which electricity is passed through cause resistance against the electricity producing heat energy. In the structure of the atoms of materials which conduct electricity the outer shell has free electrons.
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across it (providing the temperature remains constant). I am going to test this law. The four factors that affect resistance are: Lengths of the wire - the longer the wire, the more atoms there are for the electrons to collide with resulting in the loss of more energy. Thickness of the wire - the larger the cross-section, the more charge that can travel simultaneously through a given length. It is like a motorway. Material it is made up of - some materials have less resistance than others. They have fewer atoms therefore there are less atoms for the electrons to collide with resulting in a lower loss of energy.
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Electromagnets - an investigation on electromagnets, our aim will be to find out what effects the strength of an electromagnet and how it affects it.
Electromagnets are used every day in a lot of devices such as relays, circuit breakers, door/alarm bells and anything else that is found to have a motor in it. My Prediction We all know that a wire carrying a current will produce a magnetic field around it self. This means that if the wire is compressed or coiled into a solenoid then the field will be more compact and therefore very much stronger. So, if more of the wire is wrapped around the iron bar then the electromagnet should become much stronger and stronger each time.
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A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. all metals can be used as conductors. some are better than others, but they all look something like this: As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. When charged particles (current) encounter fixed particles (metal)
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The bigger the resistance of a conductor the harder it is for electric charge to flow through it. For a given voltage applied to it, the current would be less. It is like water flowing downhill in a river. If the bed of the river is smooth the water can flow easily, and more can get through on a given time. But if the bed of the river is rocky the water can't flow so easily. It will move downhill more slowly and a lot of energy is wasted - you can hear the noise and see the water being thrown up in the air.
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A greater cross-sectional area results in a smaller resistance to the flow. Resistivity is a measure of the ability of a material to resist the flow of an electric current. Resistivity is represented by the Greek letter rho, , and is measured in Ohm-metres (? m) . Resistivity is equal to the resistance R of a material such as a wire, multiplied by its cross-sectional area A, and divided by its length l. This is given in the formula: = RA/ l Usually, a material's resistance increases with increases in temperature.
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Prediction: For length of wire, I predict that the longer the wire the bigger the resistance. Scientific Knowledge: The resistance of a longer piece of wire is greater than that of a shorter wire. This is because the electrons have further to travel in a longer piece and this means they are more likely to collide with the positive ions, therefore if the electrons collide with the ion they will be slowed down considerably because they will have lost some of there energy as some of it's energy has been transferred to the ion in the collision.
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When measuring the length I will always use the same material: Constantan wire. Also I will make sure that the wire does not get hot by not measuring any less than 10cm. Also, I will always use the same thickness wire, 32SWG (standard gauge). However, when I am looking at the factor of thickness I will make sure that the wire does not get hot, that the wire is Constantan wire and that the wire is always a set length, 50cm long.
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Firstly I will attach a piece of wire to a ruler stick and pull it as tight as possible. I will then set up a circuit consisting of a power pack, voltage measure, amplitude measure and a variable resistor. I will then connect the circuit through the wire on the ruler stick, recording the results at each ten centimetre interval until I reach ninety centimetres. When doing the experiment I will keep the voltage on the power pack below six volts, avoid touching the wire as it gets hot and be careful not to cut myself on the sharp edges of the wire.
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EIN This can be shown in another way, showing the breaking down of the bonds: E = Energy H = Hydrogen O = Oxygen C = Carbon This proves that more energy will be given off when more bonds are formed. Set Variable Each time I do the experiment, I will change the alcohol. The different alcohols I will use each time are Methanol, Ethanol, Butanol, and Pentanol. Measured Variable Each experiment, I will measure the difference in weight of the alcohol before and after the experiment, to calculate the energy given off.
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Also we need to keep the voltage relatively the same which may not be possible with thickness, as a voltage which may cause the thin wire to smoulder may not even cause a current readable when passed through the thick wire. Material Different materials have different levels of resistance. Wires that have a greater number of ions in a set space will be more resistant. This is not a very good variable as there only three types of wire that can be used which is not a big enough range.
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Also the ball is made from rubber, and rubber is very flexible so it will deform for a fraction of a second. As it is a solid, it will return to its original shape when the atoms return to their original shape. The ball gains its most gravitational potential energy, when it is held at the set height. This turns to kinetic energy when the ball hits the chosen surface. This will occur until the energy is fully distributed by either kinetic or gravitational potential energy.
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I will have to switch on and off the power supply quickly because short lengths of wire got hot quite quickly that is why I will start of at 30 cm, because the preliminary experiments showed that very short pieces of wire get hot very quickly and they go red, which can be a danger in case it will start up a fire. To collect my results I will draw a table, which will show the voltage and the current measurements, and also the resistance, which can be worked out by using this formula: Resistance = volts/ampere I predict that they longer the wire the higher will be the resistance.
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