In a metal, the atoms exist as positive ions surrounded by electrons, some of which are free to move within the crystal structure. At all temperatures above absolute zero, all the particles are in constant motion. The ions held in place by strong binding forces, simply vibrate in their fixed positions, while those electrons that are free can move about place to place. Without an external electric field, the electrons rapidly and randomly move about in all directions. There is no net motion in any particular direction.
This is illustrated in the diagram. By connecting a battery, all the charged bodies (the positive nuclei, orbital electrons and free electrons) experience a force. The positive nuclei are more attracted towards the more negative potential, while the electrons are attracted towards the more positive potential. However, only the free electrons can move under the actions of this force. This force will accelerate these electrons, but their speed is limited by collisions with the metal ions.
Consequently the resultant motion of the conduction electrons is best described as a drift towards the more positive potential, which is shown on the diagram below. The free electrons are accelerated by the electric field, gaining kinetic energy from the field. In the collisions with the metal ions, this kinetic energy has been converted into vibrational kinetic energy of the ions, with the resulting increase in the temperature of the metal. This energy is dissipated to the surroundings as heat energy. This is the heating effect of Tommy Clifford 10D.
the electrical current. Individual electrons never acquire a steady velocity, but the large numbers involved can be thought as having an average drift velocity. Electrical insulators are made from materials with very small numbers of electrons, which reduces magnitude of the current to a negligible amount. Hypothesis If I double the length of the wire then the electrons will travel twice the distance. Hence twice as many collisions will take place with the atoms of the wire. Therefore the resistance will double. Resistance is the opposition in the current of the flow.
R = P1/A Where R = resistance 1 = length A = cross-sectional area P = Resistance R is directly proportional to 1. The resistance increases as the length of the wire increases because the voltage down the wire pushes the electrons; the atoms however vibrate up Tommy Clifford 10D and down making it difficult for the electrons to pass. Therefore the longer a piece of wire is the more resistance there is (see diagram below). Apparatus The apparatus that I will be using for this experiment is as follows; Crocodile clips, Voltmeter Ammeter Rheostat Plan 1.
Using crocodile clips the wire will be connected to the voltmeter, ammeter and rheostat as in the diagram 2. Both the rheostat and the ammeter will the n be connected to the energy source but the energy source will not be turned on. 3. The crocodile clips be placed 10cm apart from each other. 4. The energy source will be turned on 5. The reading on the voltmeter and the ammeter will be recorded. 6. The positioning of the rheostat will be changed twice more and the readings from the ammeter and voltmeter will be recorded. 7. Using the formula R = V/I the resistance will be worked out and recorded.
8. The steps 3-7 will be repeated by using the following lengths of wire- 10cm, 20cm, 30cm, 40cm, 50cm and 60cm. Fair Test Principals 1. The wire cannot be changed. If it was changed then the results will not back up my predictions. For instance if the wires were changed, the different rates of conductivity so the resistance would change. To stop getting these kinds of odd results the same wire must be used. 2. The length of the wire must be accurate because the results would be wrong if the crocodile clip was 17cm apart when it’s only supposed to be 10cm apart.
This reading will obviously cause misleading results. 3. The readings must be taken in the same surroundings, because if a reading is taken, pressure on the table can make difference, as the apparatus is moving. 4. After a reading is taken the energy flow must be disconnected. This is because the current flow causes the wire to rise in temperature, therefore varying the results. For this experiment each reading will be repeated 3 times to provide an average. This will provide valuable data for the later part of the investigation. Tommy Clifford 10D.
Evaluation If I did the experiment again, I would use not only the length but the cross-sectional area to measure the resistance as well. I would then repeat the experiment with different wires of different cross-sectional areas. This would ensure an even more accurate result. One thing that went wrong in my experiment, was that I did not put the voltmeter in parallel to the circuit at first, so I got completely wrong results and had to carry out the experiment again. Conclusion With reference to the graph, there is a positive correlation.
This proves my hypothesis to be correct. If you increase the length the resistance will also increase i. e. if you double the length of the wire, the resistance will double also. In conclusion I think that my experiment went very well and I gained a fair result out of it. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.