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GCSE: Electricity and Magnetism
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They can be found in electric motors and loudspeakers. Powerful electromagnets are used as lifting magnets in scrap yards. Another use an electromagnet is an electric bell used in most schools. When the switch is turned on, the current flows through the circuit and the electromagnet makes a magnetic field, therefore the electromagnet then attracts the striker (metal arm)
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, where I is a constant. Then is also constant. Hence the potential difference across the capacitor increases linearly with time. Procedure 1. The circuit was connected as shown in the figure below. The CRO was set to d.c. and the sensitivity to 1 V/cm. 2. The time base was set to any high value so that a steady horizontal trace is displayed. The trace was shifted to the bottom of the screen. 3. The capacitor was shorted out by connecting a lead across it and adjust the 100 k ? potentiometer for a suitable current, say 80 ?A.
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Variables Input: * Length of wire. * * Material of wire. * Width of wire. * Starting temperature of wire. Output: * Voltage across wire. � * Current in circuit. � * Temperature of wire. * Resistance of wire� The variable marked with a * will be varied, the other input variables will be kept constant. The output variable marked with a � will be measured. Predictions * The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal.
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Equipment List Power pack Length of wire Ammeter Voltmeter Wires Crocodile clips Results Voltage (V) Voltage Setting (volts) Length Of Wire (mm) 2 4 6 200 1.48 2.90 4.35 600 1.64 3.29 5.06 1000 1.72 3.44 5.29 Current (A) Voltage Setting (volts) Length Of Wire (mm) 2 4 6 200 1.28 2.82 4.54 600 0.72 1.46 2.25 1000 0.44 0.92 1.45 Analysis The results show that my prediction was correct. The 2V setting produced far too little numbers and some of them were decimal points.
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Resistance of a wire - a number of experiments were carried out to determine different variables affected resistance.
Single length of constantan wire 5. Double length of constantan wire 6. Triple length of constantan wire 7. Single length of constantan wire (10cm, 20cm, 30cm) The conclusion drawn * Types of wire - Comparing wires made from different materials. It was found that each different type of wire had a different resistance. Therefore, it is fair to conclude that the resistance of a wire depends upon the resistivity of the wire, i.e. its ability to resist the flow of charge. * Thickness of wire - Comparing wires which had different thicknesses. It was found out that as the thickness of the wire increased the resistance decreased.
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Set the voltmeter to 1 volts and place the lead in the 5 OHM's resistor 4. Turn to the Power Pack and record the reading on the ammeter 5. Repeat step 3 and 4 2 more times. 6. Change the volts to 3,5,7,9,11,13 and 15, remembering to only record with the 5 OHM's resistor. 7. Record the results using the 5 OHM resistor 8. Repeat steps 4 - 7 but instead of using the 5 OHM's resistor, use 10 OHM's, 18 OHM's and 56OHM's resistors 9. Clean up all equipment and analyze the results Results: Current (A)
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I will get a minimum length and a maximum range, get the volts and the amps and use the equation to work out the resistance of that particular length of wire. Preliminary experiment: 40cm Voltage = 0.06v Amps = 0.09A Resistance = 0.06�0.09 Resistance = 0.67? (rounded up to 2 D.p.) 90cm voltage = 0.15 Amps = 0.08 Resistance = 0.06�0.08 Resistance = 1.88(rounded up to 2 D.p.) This has now given me a range of lengths to do between 40cm to 90cm of wire Method (continued): I then decide to do lengths of 40, 50, 60, 70, 80 and 90cm.
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The solenoid needs to be put in upside down. Hook the spring onto the clamp and then attach the bar magnet. The bar magnet needs to be hanging down so that it is 1/4 of the way down on the magnet or 3/4 of the way down in the magnet (as shown in the diagram below). Adjust the boss clamp so the bar magnet hangs down in a perfectly central position in the solenoid. Then attach the 20g weight to the bar magnet. Connect the connecting leads into the solenoid and then connect both leads into the 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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Strategy The factor I have chosen to investigate the effect on resistance after changing the length of nichrome wire, whilst the current is consistently 0.2 amps. I have chosen this factor because if I would have chosen rho (material) I would be limited as to the things I could investigate: the highest or lowest resistance out of all materials tested. This would mean that I could only put my results in a bar chart as it is not continuous data and would mean I would be limited as to the conclusions I could extract from my findings.
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Current (A) Voltage (V) 100 7.35 0.50 200 5.83 0.80 300 5.03 1.04 400 5.15 1.24 500 5.01 1.34 600 4.83 1.50 700 4.65 1.64 800 4.23 1.62 900 4.15 1.72 1000 4.01 1.78 Theory Resistance is when electricity is passed through a circuit and is measured for finding how easy the current goes through the circuit It is measured the by finding the current that is present in the circuit and the voltage across the wire, then is placed in this formula: V= I/R Perditions My perditions are that the longer the wire the greater the resistance.
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So our cell had also a resistance that changes due to age and type of battery. The main function of it is to model the condition that reduces the current flow. In the experiment carried out we have used the following equipments: Battery (or cell) - 1.5 V Wires Switch Variable Resistors (10 items) Voltmeter Ammeter Using equipments listed above the experiment circuit was set up as shown below: By changing the resistors different values on Ammeter and Voltmeter were taken for all of them. The resistors were chosen between 0 ohms and 100 ohms. The values were measured three times each in order to check their reliability.
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Electrostatic force Electrostatic forces occur between charged objects. Objects which have like charges repel each other and objects with unlike charges attract each other. The force of attraction or repulsion depends on how much charge is on the two objects and how far apart they are. COULOMBS LAW The force of attraction or repulsion between two charged objects is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. Electric Fields Area around a charge object is a force field in which any other charged object will experience a force of attraction or repulsion.
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* Changing the thickness of the wire - - increasing the thickness of the wire will increase its resistance because there are more stationary atoms in the wire for the moving electrons to bump into. * Changing the material of the wire - different materials have a different number of stationary atoms in the wire. I will change the variable length and keep the thickness and material the same in all experiments. Method 1. I will set up my apparatus as shown in the diagram below 2.
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This will be kept constant because current will be kept constant. iii) Cross sectional area (thickness) - This will affect the resistance because as the area of the wire increases, the resistance will decrease because the electrons now have more space to travel and have better chances of avoiding collisions with the ions in the lattice and so the current can flow more efficiently. iv) Length of wire - Similarly if the wires length increases, then the electrons have a larger distance to travel.
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to the ratio of potential difference (voltage) across it (providing the temperature remains constant)", or... the current passing through a wire, at constant temperature, is proportional to the potential difference between its ends. This is the solution to working out the resistance of a wire, and is called Ohm's Law. He also put this discovery into a memorable formula: ... (V= P.D (volts), I=current (amps) & R=resistance (Ohms)). Using this formula, we can effortlessly work out the resistance by only working out the p.d and current (using a voltmeter and an ammeter), and then calculating the resistance.
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The resistance in a wire occurs because the electrons have to get past the fixed positively charged ions. So if we change the thickness or length of a wire, we change the number of ions affecting the flow of electrons and so change the resistance. Similarly, if we change the temperature of a wire, this affects the vibration of the fixed ions, and hence how much they impede the flow of electrons. In this experiment, I will be investigating how the length of a wire affects its resistance. HYPOTHESIS My hypothesis is: The greater the length of wire, the higher the resistance.
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Thickness of the wire, 2. Length of the wire, 3. Material the wire is made out of and 4. Temperature of the wire. I have decided to investigated how length affects the resistance of a wire. So, to make this experiment fair I will keep thickness, material and temperature the same at all times in the experiment. The only variable that will change is going to be length of the wire. Also to make this test fair I will keep the supply at the same voltage and will make sure that this voltage is not to high so the wire could not overheat.
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Thin wire is used in some appliances like kettles because it heats up quickly. Electrical current is directly proportional to resistance; Ohms law states that - R = V/I. Variable resistors are used in the home for light switch dimmers. When you turn the knob and the light gets dimmer you are increasing the resistance. Resistance is measured in ohms, ? and you can find resistance by using ohms law which is: This is R=V I R= Resistance of the object and this is measured in ohms. (?) V= Voltage and it is measured in volts.
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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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The wire can heat up if the current is too high, and this could cause burns, so caution must be taken when handling the wire. Apparatus: * 1 Ammeter. * 1 Voltmeter. * Wire - 100cm.(Varied Length) * 5 Crocodile Clips. * 9 leads. * 1 Power Pack. * 1 Metre Ruler. * 1 Variable Resistor. * Cello tape. Method: 1) I will tape 1 metre of constantan wire to the 100cm ruler to allow me to measure the length of wire.
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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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There is however one flaw with using wood as an energy source, and that is that burning wood produces CO2. Our demands for fuel and our worries about the rise of global warming have encouraged us to search further a field for alternative energy sources. We need renewable sources that do not pollute the planet or contribute to global warming by producing greenhouse gases. Power Sources Currently Available: Renewable Energy Sources: Wind: The wind is powered by the sun's heat energy, and is a renewable energy source that has been used for many hundreds of years, most prominently for the production of flower to make bread.
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