Views 3

Essay, Pages 5 (1041 words)

Here are the results: METAL DIAMETER (mm) AMPS Copper 0. 01 0. 39 Nichrome 0. 17 0. 99 Constantan 0. 1 0. 95 As you can see from my results, nichrome is the material which best fits my criteria. Its diameter can be comparatively much larger than that of the other two wires, whilst still having amperage of around 1amps. On the computer program we used, any increase in the diameter of the wires above that of the results in the table above, would have given a reading of above 1 amp, which is my chosen limit.

From these results I can conclude that the best diameter for the nichrome wire would be 0. 17mm because it gives amperage that is as close as possible to 1amp. It will also make it easier to average out results when finding resistance using the volts as well. Suitable wire Unfortunately, in the actual experiment, we will not have a choice of diameter for the wire. Because of this, I have conducted a second preliminary experiment to confirm that nichrome is in fact the best wire to use.

In this experiment, I kept the following variables constant:

The aim of this experiment is to find out which metal would give the lowest reading on the ammeter when the three variables above were constant. The only variable changed was the type of wire. Here are the results: METAL AMPS Copper 2. 62 Nichrome 1. 38 Constantan 1. 98 Although none of the metals with these set variables could produce a reading below 1 amp, the lowest was nichrome. This confirms that nichrome is the best wire to use in the main experiment.

The hotter the wire gets, the less accurate the final results will be as the extra vibrations in the wire will slow the path of the free electrons, which will result in an apparent increase in resistance. This inaccuracy can be minimized if the current is low. I have concluded that nichrome is definitely the best available wire for use in the final experiment. It also has the highest resistivity: The resistivity values of each wire is as follows: nichrome m If at any point in the experiment, we need to adjust the size of the current, we can do so using a rheostat.

Testing nichrome Finally I tested to see that the experiment is going to work. Using the variables that I have previously decided on. These are the results: Length (cm) Voltage Amps It is clear to see here that nichrome will be suitable for the experiment. Neither voltage nor amperage gives any very extreme readings, and it is possible to use sensible lengths of wire and get a lot of results. Results The first experiment Length of nichrome wire(cm) Voltage(V)

Current(I) in amps (A) The experiment repeated Length of nichrome wire(cm) Voltage(V) Current(I) in amps (A) Processing the results Resistance and averages of both tests: Experiment 1 Experiment 2 Average resistance (? ) Length Resistance(? ) Resistance(? ) The cross-sectional area of each wire is:Conclusion If the length of a piece of nichrome wire is increased, its resistance increases.

You can see in my graph that as I predicted, the two look directly proportional: The two increase at the same speed, and at a constant rate. This is shown in the fact that the line on the graph is a straight one. The graph I got from the main experiment shows the same trend as the one in my prediction. I also predicted that the two would be directly proportional. To a certain degree this is true of my graph, but I have tested some of my results to see how accurate this is. Length(cm) Average Resistance(? ) Predicted Resistance of double length (? ) Actual double resistance (? )

As you can see, although my results were not exact, the general trend is very clear: Resistance and length of wire are directly proportional to each other. They increase at the same rate. Explanation As I said in my prediction: Increasing the length of a wire increases its resistance. This is because in a conductive metal, the electrons in the outer shell of each atom are free to move around. An electrical current is where all these electrons are caused to move in the same direction through the metal.

Resistance is the property of a substance that restricts the flow of electricity through it, and is often associated with heat. As the electrons are passing through the metal, they are constantly colliding with the atoms of the metal, causing their course to be slowed down. The collisions cause changes of direction which dissipate energy as heat, which is why more resistant metals heat up more than metals which let electrons pass through more easily. It is easier for electrons to pass through metals in which the atoms are small and far apart, because the free electrons can pass through with less collision to slow their path.

It is most important for the metal to contain a lot of free electrons. Fewer collisions mean that less energy is transferred to heat: this is low resistance. As the length of the wire is increased, there will be more fixed atoms for the free electrons to collide with, thus slowing their course. The length of the wire and the resistance of the wire is directly proportional. If you double the length of the wire, the resistance will also double. This is because there will be double the amount of atoms in the wire for the electrons to collide with.

The fact that it would take twice as long for the electrons to pass through in a metal twice the length is of almost irrelevant consequence because electrons move close to the speed of light, and so there is no point in taking this into consideration. If the resistance of the material is increasing, then it will need an increasingly large force to push it through:

This is the voltage. The resistance (R) is how much voltage (V) is needed to drive a given current (I). R = V/I Resistance (? ) is also equal to the resistivity of the wire(? cm) multiplied by its length(cm), and then divided by its cross sectional area(cm2).