The percentage energy loss when a ball Bounces Essay Example for Free

The percentage energy loss when a ball Bounces Essay This investigation will be to determine the relationship between the length of a conductor and its resistance. The aim is to test a number of different lengths of nichrome wire to measure the resistance of each length. To ensure a safe procedure, a low voltage battery of 12 volts will be used, and the samples to be tested will be located on an insulating mat to prevent any shorts occurring. In addition a 2 Amp fuse will be placed in the circuit as a protective measure. For a fair test, all other parameters that can affect the resistance will be kept constant. These are the sample material, the diameter of the wire, and the temperature of the wire. To keep the temperature of the wire constant, it will be necessary to keep the current flowing in it constant. This is because the power dissipated in the conductor is I2R, so an increase of current by a factor of 2 will increase the power dissipated by a factor of 4, which can seriously affect the resistance. Thus only the length of the wire will be changed, and the corresponding voltage across it to give the same test current will be varied and measured. The resistance of the test sample will then be given by Ohms Law: Resistance = Voltage (Volts) ( Ohm) My prediction is that the resistance of the wire will be proportional to its length, all other variables being kept constant Equipment The equipment used for this investigation consisted of: 1) 12 volt power pack with on/off switch 2) Variable resistor (rheostat) 3) A 2 amp ammeter with digital readout to 0. 001 amp accuracy 4) A 20V voltmeter with digital readout to 0. 01V accuracy 5) Crocodile clips for connection of the test sample into the circuit and the voltmeter to the connecting crocodile clips. 6) Test samples consisting of varying lengths of 24 SWG The equipment and the circuit configuration used is shown in Fig 1. A 12-volt power pack will be connected in series with a switch, a 2-amp fuse, an Ammeter, a variable resistor and a sample test wire. A voltmeter will be connected across the test sample by crocodile clips. The test sample was connected into the circuit using crocodile clips. The voltmeter was connected across the sample into the rear of the crocodile clips. The plan will be to vary the sample length from 10 cms to 100 cms in 10 cm increments to provide a good range of results. Also to take readings of three samples for each length, and average the voltage readings to reduce possible errors. There are four factors that will affect the resistance of a wire. These are: 1. As the length of a wire increases, the resistance of the wire also increases. A variable resistor or rheostat is used to vary the current in a circuit. As the sliding contact moves, it varies the length of wire in the circuit. 2. As the cross-sectional area of a wire increases, the resistance of the wire decreases. An analogy of this is a water pipe, if the diameter of the water pipe is small the water flowing through will. Experience high resistance to the rate of flow. However if the diameter of the water pipe is large, the water flowing. Through it will experience low resistance to the rate of flow. 3. Different types of materials will affect the resistance in different ways. Materials such as copper, are very good conductors, and is used for connecting wires. Other materials such as nichrome (as used in the investigation) have a higher resistance than copper, and so is used in the heating elements of electric fires. 4. As the temperatures of a wire increases, the resistance of the wire increases as well. This is used in resistance thermometers, which use the fact that electricity does not flow so easily through a wire when the wire gets hot. Resistance is the opposition to the flow of charge. In metals, a sea of free electrons enabling it to conduct electricity surrounds a lattice of positive ions. The shorter the length of wire, the less energy is needed to move the electrons across the wire If the metal is attached to a power supply then the electrons flow through the metal but collide with atoms. Resistance is shown below in the diagram below: The resistance of a metal can be regarded as arising from the interaction, which occurs between the crystal lattice of the metal and the free electrons as they drift through it under an applied potential difference. This interaction is due mainly to collisions between defects in the crystal lattice (e. g. impurity atoms and dislocations) also play a part, especially at very low temperatures. Resistance is measured in Ohms (? ) Georg Ohm discovered that the current flowing through a metal wire is proportional to the potential difference across it (providing the temperature remains constant). Therefore: Resistance, R (? ) = Potential difference across the wire (V) I= V i R V= I x R R= V i I TABLE 1 RESULTS: Table 1 shows the data recorded and the resulting values for resistance for each length. These were those separate samples of the conductor tested for each length, and the average voltage was used to determine the resistance volume. Graph 1 plots the resistance against length for the range of test samples from 10cm to 100cm. The graph shows the data to be in very close proximity to a straight line, verifying the prediction to its length. From the best fit line drawn on the graph, the resistance per unit length of 24 SWG nichrome wire is found to be 0. 362 ohm/cm. When current passes down a wire, the wire gets heated. The moving electrons collide with ion and cause them to vibrate thus increasing the temperature ths is a waste of energy-when a current flows, heat is transferred to the air surroundingggs which explains why computers get hot in operation. However we can make use of the heating effect e. g. in fuses which are designed to melt when too much current flows e. g. in kettles. We can calculate the heat transferred per second using the following formula: Power = (Current)2 x Resistance (Watts) = (Amps)2 x (Ohms) (W) = (A)2 x (? ) Length (cm) Current (Amps) Resistance in Ohms (R=V/I) Power (Watts) From the table above we see that there is a relationship between the resistance and the current. We see that from the results table that the power (in Watts) is equivalent to the current (in amps) squared multiplied by the resistance of the wire. From the graph showing Power Vs Length, we can work out the heat transferred in one centimetre of nichrome wire. Power i Length =Thermal energy transferred (J) Length (cm). Current (Amps) Power (Watts)Â   From these results we can work out the coulombs of charge in each separate length of nichrome. This result will then allow us to calculate how many electrons had passed through the wire, which further allows us to calculate the time taken for the experiment to take place.