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Experiment plan. The aim of this experiment is to investigate how the resistance of a piece of wire depends on its length, as Ohms law states.

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Introduction

Physics GCSE Coursework – An Investigation into how the resistance of a wire depends on its length.

Background Physics –

image00.png

The Atom

Atoms are made out Protons, Neutrons and Electrons. In the nucleus there are protons and neutrons and in the outer shells of the atom there are electrons. Protons have a positive charge; electrons have a negative while neutrons have a neural charge or no charge. Protons and neutrons have the same relative mass which is one but electrons have a smaller relative mass, theirs being 1/1840.  

image01.png

Free electron model of metallic structure 
The electrons are free to move here under the influence of an electric field. The positive ions are in a sea of electrons, the electrical energy makes the electrons move and they move randomly in the space..

Electric Current in this model

The electrons are repelled from the negative terminal in the battery, since like charges repel, and are attracted ton the positive terminal in the battery, since opposite charges attract. The electrons therefore flow from the negative terminal to the positive terminal. .. If you apply a potential difference which is known as a power source and in our case a lab pack to a metal wire it creates a current. The current within the wire can be increased by increasing the potential difference across the wire.

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Middle

Variables

Variables are changing qualities within an experiment; it is any factor or condition that can exist in different amounts. Most experiments have three different types, Controlled, Dependent and Independent.

Controlled Variables:

Controlled variables are the quantities that must be kept the same if the test is to be fair.

Independent Variables

The independent variable is the variable which will be changed throughout the experiment.

Dependent Variable

The dependent variable is that which the person carrying out the experiment focuses their observation as it tells them the differences that the changes of the independent variable have on the experiment.

My Variables –

Independent

Length of the wire - I will be using different lengths of the resistance wire to calculate how different lengths of a wire change the resistance the piece of wire holds.

Controlled

I will use the same type of wire throughout the experiment - I will make sure I use the exact same roll of wire throughout the experiment because different wires have different resistances and I will keep the experiment a fair test.

The thickness of the wire will be kept the same - I will make sure that the wire I use has the same thickness throughout the experiment because the thicker a wire is the more electrical resistance it has, also keeping the wire the same thickness will help to keep this experiment a fair test.

Dependant

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Conclusion

Repeat

Length of Wire (m)

Voltage/ V

Current/ A

Voltage/ V

Current/ A

Average Current/ A

Resistance (Ω)

1.00 m

Analyse of Results

The graphs that will be plotted are current (I) against voltage (V) graphs. The current will be on the X-axis and voltage will be on the Y-axis. I will also have a line of best fit on my graph. Below is the way my graphs will be laid out. image06.jpg

Prediction

I predict that all the graphs will all have positive correlation as well as having a clear straight line of best fit going through the origin. I also predict that most of if not all my points will run through the line of best fit, and is a point does not run through the line of best fit, it would be very close. Furthermore I predict that the results will agree with Ohm’s law. It is expected that as you double the length of the wire you double the resistance of it, also it is expected that they should be directly proportional to each other. This is because when you double the length of the wire you double the amount of positive ions in the wire thus meaning that you double the amount of collisions between the free electrons and the positive ions, therefore if there are more collisions one would expect the resistance doubling.

This can be explained as if you take R1 to be 0.2m and R2 to be 0.8m the total resistance will be 1.0m as  RT = R1 + R2.

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