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GCSE: Electricity and Magnetism
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Copper would have a higher resistance than ni-crome, as the ni-crome is a better conductor of electricity that copper. Temperature- The temperature of the wire will also affect the resistance that it has. If the wire has a high temperature, then the atoms in the wire will be vibrating quickly. This will make it harder for electrons to pass through. The more heat that there is, the more resistance that there is also. Ohm investigated how the temperature of a wire can affect its resistance. Ohms law states, "If the temperature of a conductor does not alter, then the current which flows through it is proportional to the potential difference applied."
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The longer the wire, the further the current, which is a stream of free electrons, has to travel so each electron is more likely to collide with other electrons slowing them down. This is effectively resistance - the slowing down of electrons. Safety: Do not turn the ammeter above 0.25 to prevent a fire or the burning of the wire. When conducting the experiment don't touch the wire as it will be hot. After the experiment let the wire cool down as it will have some of it's heat from before hand.
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This will result in the flow of electrons being slowed down, and also more collision between the atoms in the wire and the electrons in the current. The distribution of these atoms also changes. In some materials the atoms are closely packed together in comparison to other materials where the atoms are spread out. Also these atoms will be large and closely packed together. Therefore there will be a smaller surface area for the electrons to pass through. The flow of electrons will be slowed down, and the collisions between the electrons and atoms will be more frequent.
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When the voltage is increased, the current increases. For a particular metallic conductor, the current is directly proportional to the voltage, as long as the temperature stays the same. I also found out from reading scientific textbooks that resistance is caused by the free electrons colliding with the ions in the metal lattice. Every time the electron collides with an ion, it loses energy in the form of heat and the result of this decreases the speed. Metallic conductors Metallic conductors have free electrons, which form a gas, which then can fill the entire volume of the metal.
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There are four factors that can affect resistance: * Varying length - as the length increases, the resistance increases. * Varying cross sectional area - as the cross sectional area increases, the resistance decreases. * Changing the substance - e.g. copper is a good conductor and is used for connecting wires. Nichrome has more resistance and is used in the heating elements of electric fires. * Temperature - as the temperature increases, the resistance of the wire increases. I will be investigating two of these factors. I will be changing the length and the cross sectional area of the wire. I will use nichrome wire throughout the experiment.
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Changing the cross-sectional area of the wire should also change the resistance. Making it larger lowers the resistance because the electrons would have more space to move in and so it would be much easier for them to move to the end of the wire. Changing the material means that there are different numbers of atoms and electrons so the resistance will change. If there are more atoms and fewer electrons then the resistance will increase as fewer electrons can reach the end.
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This will give me a wide range of results. From this I am now able to calculate the resistance using the following equation: R = V I can then plot my resistance values onto a graph in-order to distinguish a pattern in my set of results. Each time I will ensure that the voltage is exactly the same and I shall also make sure that nothing in the circuit changes except for the variable (length of the wire). To ensure that my results are precise, accurate and reliable I shall repeat my test until I have 3 sets of very similar results.
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Some wires 3. A power pack 4. An ammeter 5. A voltmeter 6. A piece of cotton 7. Some weights 8. A stop clock 9. Safety goggles 10. A metre ruler Method: 1. Place an electric motor on the edge of a table and tie a piece of cotton around its spindle so that the cotton is a few centimetres off the floor. Set up the motor circuit containing a voltmeter and an ammeter. 2. Tie a chosen weight at the end of the cotton so that the apparatus looks the one shown in the diagram. 3. Switch on the motor and immediately start the time.
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The atoms or ions (when electrons are lost) in metals are arranged in regular crystal patterns. The free electrons from each atom can move through this crystal structure. Due to the metal being connected to a power supply, the electrons flow in one direction towards the positive terminal- thus there is an electric current, a flow of charge (electrons). As the electrons are flowing, the energy produced is kinetic. This kinetic energy is obtained by energy being transferred from the e.m.f. (Push) supplied by the power source. I have explained that charge flows because it is pushed around a circuit by the e.m.f provided by the power source.
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across the wire ( V ) Current through the wire ( I ) V = voltage or potential difference in volts (V) I = electric current in amperes or amps (A) R = resistance to the current in ohms (W) You can remember it easier in a triangle formula: - Before starting the experiment I have decided to choose one factor that will affect the resistance of a wire. I shall do this by going through all of the factors that affect the resistance of a wire and how I would measuring each factor to find out which would be the most effective and easiest factor to measure.
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Predictions For Hypothesis 1 The resistance will nearly be directly proportional to the length of the wire. The longer the wire will be the higher the resistance will be. This is because there are more electrons, as there is more room for them. This will mean there will be more collisions. This is a long piece of wire , it is more difficult for the electrons to get through because of the number of atoms blocking there root For hypothesis 2 The narrower the wire gets the higher resistance.
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* For a small length of wire I must keep the voltage down so that it does not burn. * I should not touch the wire while it is connected to the circuit a sit would be very hot and I could get an electric shock. * To make sure no mistakes are made while setting up the equipment, as it could be dangerous if I do. * I will follow the instructions given carefully.
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First I will use 10cm of wire and connect the multimeter up properly like the picture below also I would measure the wire exactly then I would place the crocodile clips on the ends of the wire and do that for every 10cms up to 200cms and record the resistance.
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A choice of different materials will give different results of resistance. Diagram: Method: Firstly we set up the apparatus as shown in the diagram on page 1. Then we set the ammeter on 1Amp of current (I) and that is by controlling the variable resistor. We started the experiment with the Nichrome, which has 20swg of thickness, and we started with the 10cm long wire. We put it in the circuit and switched it on. We read the voltage, recorded it and solved out the resistance by the law R = - .
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This means that also there will be twice as many electrons getting through twice as many gaps. Ohm's Law V=I/R is the famous equation and law. This law states that the current through a metallic conductor (wire) at a constant temperature is proportional to the potential difference (Voltage). The size of electric current flowing trough a conductor, depends on the voltage across it, and the resistance of a conductor. If the voltage increases the current increases. Possible Input Variables Wire area Wire thickness Wire length Applied voltage Material Taught connections Cross-sectional shape Insulated Density of wire Coiled or not Temperature Preliminary Experiments Easy to measure?
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Prediction: I predict that the longer the wire is the more resistance there is because... Fair test: We will make this a fair test by keeping the voltage, type of wire, thickness of the wire the same. The only thing we will change will be the length of the wire. Method: Get a piece of wire and measure it into sections of 10cms, 20cms, 30cms, 40cms, and 50cms.
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* Resistance is measured in ohms. * A resistor has the resistance of one ohm if one volt is necessary to push a current of one amp through it. * Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. * Ohm's Law states that Resistance = Voltage over Current (R=V/I)
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The readings taken are shown in diagram 1, they show that the Phase shift is approximately 90?. They also show the VL is leading and VR is lagging. The frequency was then changed to 2 kHz the see how this effects the results and it was found that as the frequency is increased VR decreases and the Peak to Peak value of VL increases, the opposite occurs when the frequency is decreased. The readings taken when the frequency was at 2kHz is shown in diagram 2.
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To keep the experiment a fair test, I must be sure only to change ONE of the variables, all the other factors must be kept constant. If I did not keep the other factors constant the results may be incorrect and there would not be any pattern. Problems that may occur. If I were testing how the thickness of the wire affects resistance and I altered the length of the wire each time I changed the thickness of the wire, the results would not be correct.
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If this is true and possible, wind power would probably be a winner to in any race to reduce Carbon dioxide emissions in a hurry. As a result of this we would be helping the environment and economy at the same time because wind costs nothing and wind turbines do not pollute at all. There will be different experiments on different variables to investigate the factors affecting the efficiency of a wind turbine. Variables chosen have been explained in full on page .
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The crocodile clips on the wire and the position on the variable resistor were changed. 1- The apparatus was set up. 2- Two crocodile clips were put on the wire, one at 1cm and the other at 100cm. 3- Changed the position on the variable resistor three times. 4- Recorded figures on amp meter and voltmeter each of the three times. 5- Calculated the average of the three. 6- Using the averages (and R=V/I), calculated the resistance. 7- Repeated steps 1-6, reducing the length of the wire by 10cm each time, i.e., 100, 90, 80....until 10cm.
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Solar cells are thin wafers of silicon which, exposed to sunlight, produce DC electric current. Today, solar equipment for a normal household is about $15,000. For a lot of people this is too much keeping in mind that it takes many years to use electricity worth that amount. Modern photovoltaic modules are able to produce Sebastian Seidel 2 electricity at 20 cents to 30 cents a kilowatt hour (Flanigan 2). In comparison in Texas , a kilowatt hour produced by fossil energy is about 7.6 cents (Linden 1).
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Varying cross sectional area effects resistance because if the wire is thicker it allows the electrons to flow more freely, so the resistance is then lower. The temperature affects resistance because as the metal's temperature rises its constituent atoms vibrate more vigorously. This increases the amount of interaction between the atoms and the current carrying electrons. The flow of electrons is impeded, increasing the resistance. The length of a wire affects resistance because the longer the wire, the more particles there are to get in the way of the flowing electrons.
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* Changing the current. * Changing the thickness of the wire. * Changing the length of the wire. * Changing the material of the wire. * Changing the temperature. These variables are all viable to use except changing the temperature of the wire because this is very difficult and time consuming. Changing the length of the wire is very accurate and changing the current is easily done because I would have to slide the variable resistor back and forth to change it. Changing the thickness of the wire is one of the most reliable variables because temperature, current or voltage can affect it.
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The wire I will use will be consistine. I will be making the wire shorter as the investigation moves on, but I don't want to make the wire too short otherwise it'll just melt (see 'Pre-test'). I will test each length of wire three times and find the average of the three. I will need to consider safety during the investigation. To keep everything as safe as possible I will not touch anything metallic whilst the power pack is turned on. I will not cut the Consistine to a certain length. I will also wait for a while until the wire cools otherwise I may burn my hand.
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