Physics Investigation

– Resistance Of Wire. Essay, Research Paper

Aim: -To find out what factors affect the resistance of a wire (besides current of temperature.) We must use two different variables. Variables: -VariablesChosen Variables Length of wire. Thickness Type of wire.Chosen Variable: -I have chosen length of wire as one as my variables because it will give me a good range of results. I will be able to compare the results from the shortest wire to the longest. I will start at 100cm then I will take 10cm off each time until I get to 50cm. (100,90,80,70,60,50cm) The type of wire will also give me a good range of results because I will be able to see if the difference in thickness of wire makes a difference and if the different type of wire makes a difference. (E.g. aluminum and copper.) The thickness will range between 0.71mm and 0.20mm. So I will do as many different types of metal that I can do with in the allotted time.Prediction: -For preliminary work, we tested how the temperature of a circuit can affect the resistance of a bulb filament. We altered the temperature of the wire by changing how much power passed through the wire ? using a rheostat. We found out that the longer the wire the higher the resistance. We used this circuit:Greatly exaggerated in size we have a lattice of tungsten ions. These are positively charged, and vibrating fast, e.g. average speed several hundred m/s. Electrons are free to move about, pushed along by the battery, resisted by tungsten ions that vibrate more and hinder the electrons. Therefore resistance rises as the filament gets hotter but in this experiment as the length increases the resistance increases.As the electrons in an electric current move around a circuit, they bump into the atoms in the wires through which they pass. Atoms of different elements impede the electrons by different amounts. For example, electrons pass easily through copper wire, but much less easily through tungsten wires. We say that copper has a lower resistance than nichrome or tungsten. This is why copper is used for the connecting wires and cables in electrical circuits.When an electric current passes through thin nichrome or tungsten wire, the electrons cannot flow easily. They collide with the atoms in the wire, which vibrate more quickly. This causes the wire to warm up. If the resistance of the wire is high and the current is large, the wire may get red hot. Conductors which provide a high resistance are called resistors.This can be linked to the Ohm?s law. The voltage across a metal conductor is proportional to the current through it, provided the temperature stays constant.Can be written as:V IBecause V is proportional to I, we can say that:V/I = a constantOhm showed that doubling the voltage doubles the current. Treble the voltage will give treble the current, and so on. The larger the resistance, the greater the voltage needed to push each ampere of current through it. This led to the definition of one ohm:A resistor has a resistance of one ohm, if a voltage of one volt will drive a current of one ampere through it.Th resistance of a resistor is the voltage per unit of current, i.e. RESISTANCE = VOLTAGE (volts) (ohms) CURRENT (amps)R = V/ITherefore I predict that the resistance of the wire will increase as the length increases because each electron must travel further throughout the wire and are therefore exposed to more ions and electrons which is equivalent to more resistance. For type of wire I predict that the thicker the wire the smaller the resistance. For type of wire, I predict that the thicker the wire the less resistance and the thinner the wire the greater resistance.I predict that the graph will look like this: -Apparatus: -Ammeter. Rheostat. Battery Pack. (6 volt pack max) Voltmeter. Unknown resistance. 6 wires.Method: -Set up apparatus just like circuit shown in the diagram. You will need a voltmeter, ammeter, rheostat, battery pack (6volt pack), six wires and a unknown resistance. Measure out the pieces of wire to a length of 102cm. I will make sure there is 100cm in-between the clips by making the wire an extra 2cm long and at either end I will measure in exactly 1cm and place the clip their. This will apply when I make the wire shorter. (start at 102cm, then down in tens to 92cm,82cm,72cm,62cm,52cm) When you measure the piece of wire lay it out on a one-meter ruler and hold it and one end and count in the appropriate number. You can re measure it if it is not the correct number. The wire must be straight when being measured. Coil the wire around the pencil and attach to circuit. Make sure no crossovers. (The circuit will short circuit if there are crossovers) Take readings form ammeter and voltmeter. Do three repeats to improve accuracy. Do the repeats by altering the rheostat. One from either end and one from the middle. Record results again. Repeat with different length wire. When doing different type of wire as the variable measure it out to 102cm each time and again measure in 1cm from each end and place the crocodile clips on 1cm in. Then do the same three repeats using the rheostat and then change the type of wire. I will be using the thinner wires so that is why I have gone under 100cm in-between the clips. When attaching the wires make sure that the wire is not long and thin because it will have no amp reading. If the wire is short and fat it will have no volt reading. I feel that doing three repeats will be sufficient because it is a fairly accurate experiment so I think three repeats will be enough.When doing type of wire because the thickness is in Swg I will need to know it in mm: -Swgmm 220.71 240.56 260.45 280.37 300.31 320.28 340.24 360.20 Diagram: -Fair Test: -VariablesConstantsThings to change Length of wireVolts (Apart from the repeats on the rheostat)Length of wire. Type of wireVolts (Apart from the repeats on the rheostat)Type of wire. (Vary the thickness)To ensure that the experiment is fair I will: -Make sure that there are no crossovers in my piece of wire so that it does not short circuit. Make sure that I mark with the wire cutters exactly where I muse clip the clips. (1cm in from each end.) I must record the results accurately. I must do three repeats using the rheostat. I must select the correct amount of volts. I must make the wire the correct length.Results: -Length of wire: -RepeatLength (cm)Voltage (Volts)Current (amps)Resistance (Ohms) 1231001001000.300.600.90 0.22 0.34 1.171.5361.3761.698 1239090900.300.600.90 0.46 0.35 1.331.5521.7860.667 1238080800.300.600.90 0.54 1.27 1.191.1950.2640.411 1237070700.300.600.90 1.54 0.43 0.880.5561.3951.023 1236060600.300.600.90 0.59 1.16 1.600.5080.5170.563 1235050500.300.600.90 2.12 1.17 2.970.2370.5130.303Type of wire: -Repeat Type of wireVoltage (Volts)Current (Amps)Resistance (Ohms)Average Resistance (Ohms) 123Nickel ChromiumNickel ChromiumNickel Chromium0.500.700.907.3486.8977.3250.0680.1010.1230.097 123AluminiumAluminiumAluminium0.300.400.500.3650.3980.4230.8221.0051.1821.003 123ConstantanConstantanConstantan0.300.600.901.2381.2371.4690.2420.4850.6130.447 123GriffinGriffinGriffin0.300.600.900.871.782.650.3450.3370.3400.341 123MaganinMaganinMaganin0.300.600.900.190.260.341.5792.3082.6472.178 123BrassBrassBrass0.300.600.900.470.520.960.6381.1540.9380.910Conclusion: -By looking at my results I can see that the longer the wire the greater the resistance, so the shorter the wire the smaller the resistance. Also I can see that the thicker the wire the smaller the resistance so the thinner the wire greater the resistance. When using type of wire as me variable I found that Maganin had the greatest resistance and that Nickel Chromium had the least resistance. ( The final order was Maganin with greatest resistance then Aluminium, Brass, Constantan, Griffin and Nikel Chromium.) The only trends are that the thicker the wire gets the smaller the resistance. The longer the wire gets the greater the resistance. Also doubling the voltage doubles the current. Treble the voltage will give treble the current, and so on.All of this is because; Greatly exaggerated in size we have a lattice of tungsten ions. These are positively charged, and vibrating fast, e.g. average speed several hundred m/s. Electrons are free to move about, pushed along by the battery, resisted by tungsten ions that vibrate more and hinder the electrons. Therefore resistance rises as the filament gets hotter but in this experiment as the length increases the resistance increases. As the electrons in an electric current move around a circuit, they bump into the atoms in the wires through which they pass. Atoms of different elements impede the electrons by different amounts. For example, electrons pass easily through copper wire, but much less easily through tungsten wires. We say that copper has a lower resistance than nichrome or tungsten. This is why copper is used for the connecting wires and cables in electrical circuits.When an electric current passes through thin nichrome or tungsten wire, the electrons cannot flow easily. They collide with the atoms in the wire, which vibrate more quickly. This causes the wire to warm up. If the resistance of the wire is high and the current is large, the wire may get red hot. Conductors which provide a high resistance are called resistors.This can be linked to the Ohm?s law. The voltage across a metal conductor is proportional to the current through it, provided the temperature stays constant.Can be written as:V IBecause V is proportional to I, we can say that:V/I = a constantOhm showed that doubling the voltage doubles the current. Treble the voltage will give treble the current, and so on. The larger the resistance, the greater the voltage needed to push each ampere of current through it. This led to the definition of one ohm:A resistor has a resistance of one ohm, if a voltage of one volt will drive a current of one ampere through it.Th resistance of a resistor is the voltage per unit of current, i.e. RESISTANCE = VOLTAGE (volts) (ohms) CURRENT (amps)R = V/ITherefore I predict that the resistance of the wire will increase as the length increases because each electron must travel further throughout the wire and are therefore exposed to more ions and electrons which is equivalent to more resistance. For type of wire, I predict that the thicker the wire the less resistance and the thinner the wire the greater resistance. My prediction was correct that the longer the wire the greater the resistance. The Evaluation: -I think that I carried out the method accurately so I got accurate results. I think that three repeats were sufficient. I feel that there were a few inaccurate results but not inaccurate enough to call an anomaly. The method was quite accurate but I felt that some of the wires were too thick and short and thin and long so the readings on the ammeter and voltmeter where not what they where meant to be. But because I left the same wires in the circuit it did not affect the trend of my results. All of the wires that join up the circuit could have been the same length and thickness. Some of the wires may have had different resistances, which may have affected the results. To improve the experiment I could have used a higher voltage and used thicker longer variables. Overall my results and theory supported my conclusion. I am confident that my results are accurate enough to be able to draw up a firm conclusion. If you had a crack in you house on the wall and you wanted to find out if it was getting wider. Set up apparatus just like circuit shown in the diagram. You will need a voltmeter, ammeter, battery pack (6volt pack), six wires and a piece of Measure out a piece of wire at 102cm and mark in 1cm at each end then clip it right on the 1cm mark. When you measure the piece of wire lay it out on a one-meter ruler and hold it and one end and count in the appropriate number. You can re measure it if it is not the correct number. The wire must be straight when being measured. Place the wire over the crack glue the clips to the wall. Make sure no crossovers. (The circuit will short circuit if there are crossovers) Take readings form ammeter and voltmeter. Do three repeats to improve accuracy. Do the repeats by altering the rheostat. One from either end and one from the middle. Record results again. Repeat with different length wire. You could stick the wire across the crack and measure the resistance. The wire would be floppy at the moment. You could then come back after a month and measure the resistance again. If the resistance had increased the wire would have got longer. Therefore the crack would have widened. The apparatus will rest on the floor.