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GCSE: Electricity and Magnetism
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- Marked by Teachers essays 19
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According to Ohm's law, the resistance falls in the LDR as the current throughout the circuit increases. The reason for this increase in current is due to the greater number of charge carriers in the semi-conductor inside the resistor. In this case, the charge carriers are electrons. This increased number of electrons when light intensity increases, raises the semi-conductor's Conductivity and therefore lowers its Resistivity as the two values are inversely proportional. It is only reasonable to say that as the current through the circuit increases, so too will the voltage across the LDR. A Quantum Explanation for the behaviour of an LDR I have already said that the increased voltage across an LDR is due to
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Current- this will be kept low so will not become hot, and effect resistance. A set value will be decided. Temperature-the higher the temperature the wire is at the more resistant it becomes and will be cheap low enough not to let the temperature increase. Equtions; R = V I Resistance is equal to Voltage/Current R L C.S.A Circuit; Outline Plan; * The variable I will be changing is "length of Constanton wire." * I will find the length in a pre-test. I will also combine the to together to find out the range of length with the wire type.
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This is called strain. Strain is the amount of deformation a material experiences per unit of original length in response to stress. Change in length x Original Length L The same definition and symbols are also used for tensile and compressive stress. As strain is a ratio of two lengths, it has no units and is therefore dimensionless. When stress is applied to a material, strain is produced in the material. The strain is proportional to the stress provided the stress does not exceed a limit known simply as the limit of proportionality.
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In this coursework, I will be analyzing and proving that although metallic conductors are good conductors of electricity, they are affected by resistance.3 star(s)
Thus all metals are good conductors of electricity. But some metals have more free electrons, so they are better conductors, since more electricity can be passed. EXISTENCE AND MOVEMENT We now come to our next question, 'How does a wire conduct electricity?' We all know now that the there are free electrons in any piece of metal, but it still can't conduct electricity, if we just leave it by it self. This is because; there is no potential difference. If we examine a piece of metal closely, it turns out that the free electrons form a cloud, or a sea of electrons.
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Graphs This is what I think my two graphs will look like: P/W P/W Voltage/V Voltage2/V2 1. The first graph will look like this because as the voltage increases, the current also increases. As they both increase, the power increases by a greater amount each time so the graph will have a curved line. 2. The second graph will look like this because as the power and voltage2 are proportional. This is shown by the equation P = V2/R. If the resistance of the light bulb remains constant, power and voltage2 increase proportionally.
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There are many factors that could be taken in to account. I need to pick the right one because it is vital that I pick the correct one. The spider gram on the next page shows all the possible factors that I could use in the investigation. For the power supply in the circuit I chose to use a 24 Volt Power Pack set to A.C. 24 volts is a large voltage and I can see the changes in the readings because they are not too small.
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This is shown in the diagram above. This is the basis of my investigation. The factors that alter resistance are: * The diameter of the wire - the bigger the wire the lower the resistance because there is a larger amount of space for the electrons to move which means there are less collisions with the ions. * The length of the wire - the longer the wire the higher the resistance because there is a smaller amount of space for the electrons to move which means there are more collisions with the ions.
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All materials have some resistance, except for superconductors, which have a resistance of zero. Objects such as wires which are designed to have low resistance so that they transfer current with the least loss of electrical energy are called conductors (see Figure 1). On the other hand, objects which are designed to have a specific resistance so that they can dissipate electrical energy or otherwise modify how a circuit behaves are called resistors (see Figure 2). Conductors are made from metals (in particular copper and aluminium)
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What factors affect the resistance of a wire?The reason why the length of the wire affects the resistance of the wire is because if there is more wire for the electrons to travel down, they are impeded by more stationary atoms
The reason why the thickness of the wire affects the resistance of the wire is because depending on the thickness of the wire, it could allow or prevent more electrons to flow through the wire; therefore in theory if the wire is thinner there should be a greater resistance. The reason why the material the wire is made of affects the resistance of the wire is because depending on the density of different wires, some are more dense and should in theory, resist the amount of electrons able to run through the wire as there are more stationary atoms blocking the path, therefore if the wire is less dense it should resist less.
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Resistance of a wire. Jack has been given a second hand D.C. dynamo and lamp. He wants to attach these to his bicycle and produce most light without blowing the bulb. What wire should he use?
We also had a voltmeter in parallel to the wire we were testing. The readings we take off the ammeter and voltmeter allow us to figure out the resistance using a simple equation: Voltage � Current = Resistance. Our circuit looked like this... A variable resistor allows us to control the current going through the circuit. We needed to keep it as low as we could to avoid a heating effect in which ohms law would not take place and our results would not be accurate. Type Of Wire Current (I) Voltage (v)
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The equipment we used to make our results accurate is an ammeter which measured the current of the electrons through the wire. We used a voltmeter to measure the potential difference across the wire. We also used a variable resistor so that we were able to control the voltage to help us get our expected results. The current is changed throughout the experiment so that we could get more than once for each length so that we get a good average.
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We are going to be investigating the resistance of a wire when measuring at different lengths. We will be using four types of wires which are: * Copper, * Manganese, * Constantan * Nickel chrome. We are going to be measuring the resistance at six different lengths: * 10 * 25 * 40 * 55 * 70 * 90 The swg of the wire will be 28 for each experiment which will keep it a fair test. Also, we will repeat our experiment 5 times for each length as this way our results will be more reliable and more accurate.
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Some materials are better conductors than others. * Length- As we will find out in the following investigation, the longer the wire the higher resistance. The electrons collide with fewer ions in a shorter wire than in a longer one. * Thickness- The thinner the wire the more resistance it has. * Temperature- Metal ions vibrate more when it is hotter so the collisions with electrons are more likely, this means that the higher the temperature, the higher its resistance. Equipment The Equipment needed for this investigation is: - 2 x meters - one multimeter will measure the voltage (voltmeter)
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The higher the temperature, the greater the vibration. Electric current is the flow of free electrons through the material. As the electrons move, they collide with the vibrating atoms, so their movement is hampered. The more the atoms vibrate, the greater the chance of collision; this means that the current is less and the resistance is greater. All materials have some resistance to a flow of charge. A potential difference across the material causes free electrons inside the conductor to accelerate. As the electrons move through the material, they collide with the atoms of the material which are in their way.
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R=K x L/A R= Resistance - measured in Ohms (?) K = K factor (the type of material) L = Length of wire- measured in cm or m A = Area of cross section Current is the flow (movement) of electric charge. Electric current is measured using an ammeter and is measured in "amps". Symbol for amps is "A". I=Q/T I = Current- measured in 'amps' Q = Quantity of charge- measured in 'coulombs' T = Time - measured in 'seconds' Voltage is the measurement of the potential for an electric field to cause an electric current in an electrical conductor, specifically; voltage is equal to energy per unit charge.
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* Do not touch the wire at any time as risk of getting shock. Method: 1. Collect apparatus 2. Set apparatus as shown below : 3. Use the crocodile clip to connect the current to the meter stick, at the range of 10cm. 4. Turn on the power pack and record the ammeter and voltmeter read. 5. Connect the crocodile clip to the 20 cm of Nichrome. Turn on your power pack and record what the ammeter and voltmeter say.
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across the wire and the ammeter is used to find out the current through the wire. Then the resistance can be calculated using the formula with the two meter readings. Georg Ohm discovered that: 'The current through a metal wire is directly proportional to the p.d. across it (providing the temperature remains constant).' This is called Ohm's law. Materials that obey this law are called ohmic conductors. Factors: There are four factors that affect the resistance a wire has. These are: - Type of wire - Length of wire - Cross sectional area - Temperature All metals are good at conducting electricity but some are better than others.
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The type of material that will be used will be decided upon by preliminary tests that will be taken. The preliminary tests will involve using different materials as part of a test circuit. A similar circuit will also be used in the actual experiment. Another constant is the thickness of the wire. The thickness of a wire always affects resistance because the thicker the wire is, the lower the resistance will be. During the preliminary tests, the thickness of the wire will also be tested to see what sort of thickness is the most appropriate to use for the main investigation.
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Wire length: If the wire is longer, then the resistance will be higher because the electrons will have a longer distance to travel and so more collisions will occur. Because of this the length increase should be proportional to the resistance increase. 4. Cross-Sectional Area of the Wire: If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Because this increased space between the atoms there should be fewer collisions, and more current will flow.
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Width of wire can have dramatic affect towards resistance, which is because the width is inversely proportional to resistance; therefore if you increase the width the resistance will decrease. Because there will be more space for the electrons to move around this should therefore decrease the amount of collisions. But if the wire is thin the opposite reaction will happen, less space the increase rate of resistance. Temperature has a big impact upon resistance whether the wire is hot or cold; if the wire is cold the atoms in the wire move around slowly, it also means the wire will have a low resistance.
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Carbon is not a metal, it is a semi-conductor and it does not behave like a wire when hot. Semi-conductors are poor conductors when cold but are better conductors when warm. Carbon is found in several forms and they have very different properties. The most common form is graphite, and one of the good things about graphite is that it conducts electricity. It is also very soft, so is perfect wherever there is a need for a soft material that conducts electricity (conducting putty.) Variables: Possible Variables I could investigate are: * The shape of the cross section of the putty - e.g.
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To investigate how the piece of resistance wire depends on length and to find the length of wire needed to make the required resistors
and finally at 100cm, the resistance will be 7 ?. They wouldn't collide as much in a shorter wire than in a longer wire because of this piece of information. Resistance should also be proportional to the length of the wires, so if you double the length, the resistance will also double. Apparatus: -Leads -Ammeter (of scale 0amps to 1amp - this is because of the results from my preliminary work, which showed that most results came in and around this scale, and so it would make my results more accurate if I used this sort of scale)
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To heat the water even faster a powerful electrical heater is inserted into the boiler which heats water faster, an immersion heater. A standard thermostat, which ensures no overheating of the water tank, relies on a bi-metallic strip. This is built on the principle that not all metals expand at the same rate and bends when it is hot. The bi-metallic strip is not suitable however for the purpose we require. We require an accurate reading of the temperature to ensure a hot bath is achieved and also the sensor could act as an energy saving device stopping unnecessary over heating of the water inside.
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All other variables will be controlled and kept constant throughout the whole experiment. The following are the variables which will have to be controlled: Temperature- Considering that "superconductivity" only occurs when we cool down metals to extremely low temperatures and no resistance occurs, there would have to be very big temperature changes in order for temperature to play a role in the resistance of the wire. Therefore no drastic measures have to be taken in order to control temperature since any temperature changes in the air will not really affect the resistance.
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Diagram For my experiment this is a diagram of how the experiment will be set up. Apparatus These are the apparatus I will be using for my experiment. * voltmeter * ammeter * ruler * battery * power supply * extra wire * variable resistor * connecting wires Method This is the method of what I will be doing for the experiment. 1. Set up apparatus as shown in diagram above 2. Make sure the ammeter reads 0.5A (I will explain in the preliminary work)
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