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GCSE: Electricity and Magnetism
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Fossil Fuels versus Renewable Energy Coal, Gas and Oil are fossil fuels, so called because they have been formed from the remains of rotted fossilised prehistoric
It is a fact that life in the 21st century cannot exist without electricity. Daily routine would grind to a halt, so when fossil fuels eventually run out, although it will not be in our lifetime, it is essential for future generations to have an effective, sustainable energy source. Along with the environmental issues come some hidden political aspects over money and power. In elaboration to this point major political powers such as the United States find it essential to have a foot in the middle east, where there is a rich oil supply, to ensure they have this energy source for years to come.
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Resistance is measured in Ohms. George Ohm revealed that the electro-magnetic field of a circuit is directly proportional to the current flowing through the circuit. He also discovered that circuits some time resist the flow of electricity, he named this force resistance. His rule for working out the resistance is: The following factors influence the resistance of a wire: Thickness of the wire - the wire is similar to a corridor in a busy place and the electrons flowing through the wire are similar to the people going through the corridor.
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Each region of the EM spectrum has different uses in everyday life. radio waves These are used for transmitting radio signals, phone signals and television
X-rays These are used for medical purposes in hospitals, to look at our bones. Gamma rays These are emitted by radioactive substances, and are also used for killing some cancer cells. Each regions wavelength also relates to what it is used for. For example, radio waves are used for transmitting radio signals because they have a long wavelength, and can therefore travel further without being disrupted. Also the reason we can see visible light is because of its wavelength. radio waves have a long wavelength and low energy, this makes them safe for us to use in the way we do, however gamma rays have a short wavelength and high energy, this is what makes them very dangerous.
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Resistors are devices specially made to provide resistance. They also give off heat when a current passes through it, but this isn't their job. In some circuits, they are used to reduce the current. In TV or radio circuits, they keep currents and voltages at the levels needed to make other parts work properly. There are different types of resistors a few are listed below. o Variable resistors o Rotary resistors o Slide resistors Variable resistors Variable resistors are used to control the strength of an electric current.
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I will improve what we did in the prelim by controlling all the variables i.e. I will keep the power supply at one amp, I will allow the wire to cool and I will use the same thickness of wire. Step by Step Plan: 1. Set up the equipment as shown in the diagram. 2. Set the crocodile clip at a certain length, start at 10 cm.
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This may make it easier for the electrons to pass through, or harder, resulting in more collisions. In wire X, the electrons can pass through the middle of the wire, without too many collisions. However, in wire Y, the arrangement of the atoms mean that the electrons would bump into atoms located in the middle of the wire, creating more resistance. Temperature Ohm's law is only correct when the temperature is constant. Therefore, temperature must affect resistance. Temperature changes due to changes in kinetic energy. The higher temperature an atom has, the more kinetic energy it has, and the more it moves.
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The length of the wire affects the resistance as of the distance the current must travel. A longer wire would have more resistance then that which is shorter. Thus, the prediction here is that although there will be different resistances between two wires of different dimensions, the overall resistivity calculated for nichrome will be the same, as it is calculated per metre for a uniform cross-sectional area. Equipment * 0.5 m (32 gauge) Nichrome wire * 1 m (28 gauge)
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If the cross-sectional area is doubled the resistance will halve. This is because if the cross-sectional area is doubled there is an increase of space between atoms for the electrons to travel through. Due to this increased space between the atoms there should be less collisions. My graph should show that the cross-sectional area is inversely proportional to the resistance. The diagrams below show my prediction and should explain it more clearly: Diagrams: Figure 1 These diagrams show how the theory of resistance is affected by the alteration of the length of a wire.
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We use 39AWG constantan wire. However if the wire is thicker the less resistance there will be as the free electrons will have more space. Apparatus: * Goggles (see Safety) * Constantan wire * Power Pack * Voltmeter * Ammeter * Wires (plastic coated) * Crocodile clips (for plastic coated wire ends) * Meter Ruler Circuit Diagram: Preliminary Experiment The preliminary experiment makes sure I know how to set up the experiment safely and also get used to some Safety Rules ( see Safety)
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The resistance of a wire depends on certain factors. Some of these variables are listed below: Length of wire Diameter of wire Temperature at which wire is at
� The potential difference across circuit. � Cross sectional area 1) Temperature When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms that are in their pathway. This increases the amount of collisions therefore there is more resistance.
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* Resistance is anything in the circuit which slows the flow of current down. There would be a balance in a circuit. The voltage is trying to push the current around the circuit and the resistance is against it, the relative sizes of the voltage and resistance decide how big the current will be. If you increase the voltage, then more current will flow. If you increase the resistance, then less current will flow. People normally believe that current flow from positive to negative. However after electrons were discovered it is now decided that current flow from negative to positive as electros are positively charged.
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"Ohms Law" is a simple formula, which can be used to calculate resistance, potential difference (voltage) or current in an electrical circuit. Potential Difference (Volts) = Current (Amps) � Resistance (Ohms). So in order to calculate resistance the formula is rearranged as below: Resistance (Ohms) = Potential Difference (Volts) / Current (Amps). Factors affecting resistance There are four main factors affecting resistance: * As temperature increases, the resistance of a wire increases. This is because as the temperature rises, the particles of the wire move about, therefore the electrons have a higher restriction, resulting in a high resistance.
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The reason we are performing this experiment is because we want to see if 'The Length of the Wire' has an affect on the resistance of the wire. Length will be the variable in this experiment. Prediction I predict that as the length of the wire is increased the resistance will increase and as the length is decreased the resistance will do the same. I believe this because I know that if the electrons in a current have further to travel then the resistance will increase.
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Prediction I predict that the longer the wire, the higher the resistance. This is because there will be more collisions in a longer piece of wire. Therefore, more energy is going to be lost in these collisions. Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire, you are doubling the amount of collisions, meaning you are doubling the loss of energy. Preliminary Work For our preliminary work, we measured the current passing through a copper wire of lengths 10cm and 50cm at 1 volt and 5 volts.
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Factors - I will be changing the length of the wire Prediction - I predict that the longer the wire the higher the resistance
the same wire Apparatus - The apparatus I will be using are: � Lab pack � Ammeter � Voltmeter � Crocodile clips � 1 Metre nichrome wire � Metre ruler � Switch You're Experiment - 1.
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The ranges of lengths I will be using for my final investigation are: 0.2m, 0.4m, 0.6m, 0.8m and 1.0m. Fair Testing: The variable I am testing for this investigation is the length of the wire I will be using. * I will be keeping the following things the same: Multimeters, Wires Current flow through the circuit. Type of wire- nichrome Power pack Voltage on power pack (6v) Number of bulbs (1) * The only two things that will be changing in the experiment are: The voltage through the circuit The length of nichrome wire. Safety: * Do not switch on power pack until the circuit is complete, and you have checked it.
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- Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase. - Wire width: If the wire's width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
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In this experiment we have been asked to find out whether the length of wire in the circuit will effect the resistance..
Before I could do the test I have to decide on a lot of things. I had to decide how long and short I would make the wire; as if I make it too short it would melt but if I made it too long the readings would be inaccurate. I had to find out the diameter of the wire I would be using.
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In this experiment the resistance change in a wire will be investigated. I will be investigating if the thickness or cross-sectional diameter of the wire affects the resistance.
Diagram Method ==> Set up the apparatus as shown above. ==> Measure a piece of wire to 50cm ==> Clip on the crocodile clips at each end ==> Turn the power pack to 12V ==> Now write down the readings from the voltmeter and the ammeter ==> Repeat with different thickness' of wire ==> Repeat the whole experiment 5 times so an average can be taken ==> Work out the resistance (R=V/I) Fair testing To keep my experiment a fair test I will bee using the same equipment and making sure that the length of wire I use stay the same length.
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Hypothesis: I think that as the length of wire increases so will the resistance. I think this because the resistance under constant temperature conditions is directly proportional to the length of wire and inversely proportional to the cross-sectional area. Plan: In this experiment we will be varying the length of the wire. This will allow us to see if the length of wire affects the resistivity in any way. We will calculate the resistance by dividing the voltage by the current (V=IR). At every 5 centimetres, we will be measuring the voltage and the current.
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Temperature ? Length of the wire ? Thickness of the wire These are all factors that would affect resistance, but I am only going to investigate one factor. Chosen variable The variable that I have chosen to use in this investigation is the length of the wire. I have chosen to use this variable as it would be the easiest to do as the length of wire is easy to measure and would probably give the most accurate results due to this.
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* 6 leads Step by Step 1. Collect the required equipment together 2. Set up the circuit 3. Positive connects to the 0cm mark and the negative will connect to 10cm. 4. Switch on circuit 5. Record the voltmeter and ammeter readings. 6. Repeat 3 times for accuracy and get an average. 7. Move the negative wire to 20cm and then repeat. 8. Repeat this all the way up to 60cm. Fair test All things need to be kept the same in an experiment except the one key variable, in this case the length of the wire.
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The higher the trolley is elevated the greater the potential energy is. By using the gravitational potential energy formula we can see that as the height of the ramp increases so does the potential energy. This is because mass, gravity and height are all related and their combined product is GPE so if the height is a smaller unit, then the potential energy will decrease and if the height was a bigger unit the potential energy will increase. Since the potential energy of an object is directly proportional to its height above the zero position, a doubling of the height will result in a doubling of potential energy.
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The colour codev BROWN to the LIVE (L) terminalv BLUE to the NEUTRAL (N) v GREEN/YELLOW to the EARTH (E) terminal
at each end. Left Pin: Neutral Centre Pin: Earth Right Pin: Live * For safety reasons I connected I.E.C end first because if were to connect the plug and I would have fitted everything and then plugged it into the mains, somebody near me or even me would touch it would have a shock instantly. * Fitted the outer sheath into the I.E.C connector making sure it was clamped under cable clamp-arranged inner conductors adjacent to appropriate terminal. * First I take the 3 core mains cable and I use the wire stripper to cut them to size 10mm (1cm)
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Prediction: I predict that, as the length of the wire increases so will the resistance. I think this will happen because as the wire gets longer the current has more atoms to get through. If the length of wire is twice as long, the resistance will double e.g. Length of wire: 10cm Resistance: 4Ohm Length of wire: 20cm Resistance: 8Ohm Apparatus: Power pack - this provides energy for the circuit 3 wires - are used to connect power pack to resistance board Resistance board - nichrome wire is tied to it and the board is used to work out the length of wire Nichrome wire (0.2mm)
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