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Does the length of a wire affect its resistance?

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Introduction

ZESHAN HAFIZ KHAN

HALL GREEN SCHOOL

SCIENCE COURSEWORK – PHYSICS

GCSE Science Physics Coursework     “What affects the resistance of a piece of wire?”

Does the length of a wire affect its resistance?

Aim

The aim of the whole thing is to find out “does the length of a wire affect it’s resistance” we will find this out by using 3 metals, cutting them in 3 pieces one 10cm, 20cm and 30cm and then we will find out the resistance of them wires we will keep doing this to the same length wire and same metal for 5 times to find it is done accurately.

This was the diagram that we had used to find out our question, the circuit was very easy to set up and find out which wires went where, it was very symbol all it was a circuit going around in a circle.

The APPARATUS that I will use in this experiment are:

  • Ruler
  • copper
  • 3 cells (2 x 1.5 volt cells)
  • 3 wires
  • ammeter
  • voltmeter
  • chrome
  • managanin

INDEPENDENT VARIABLE: the independent variable is the thing that I will be changing, for this experiment it will be the length of a wire as this is what we are going to change i.e. by increasing or decreasing the length.

DEPENDENT VARIABLE: this is the part of the experiment that will be depending on another factor that of the length of a wire. I will have no control over the dependent variable. The dependent variable will be the resistance as this is what will change with the length of wire it is dependent on length of wire.

FAIR TESTING:

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Middle

                     R = R1 + R2   where R equals total resistance of the circuitimage06.png

R1 = 4.7 ohms

R2 = 10 ohms

A = 0.14A

V = 2.21v

As we are using Constantan wire as a resistor when we increase the length of the wire the resistance should work how resistors in series work. This means that when we increase the length of wire (or add a piece in a series circuit) the resistance should increase too. Due to the increase in the number of atoms and ions between the two terminals it takes the electrons longer to get from one side to the other. For example if we double the length of the wire the resistance will double and the current will halve. Our graph at the end should look something like this:

image07.png

                                                                                            Length

                                                                                                  Resistance  

The length and resistance should be directly proportional to each other. So the graph will be diagonal through the origin.

Pre-test

We have done a pretest so that we can decide which thickness of wire to use, and what the highest current we will use will be. From an earlier experiment we know that the thicker the wire is the less likely it is to affect the resistance, therefore it will be ideal to use a thick wire instead of a thin one in our experiment. Therefore we have chosen to use a wire that measures 24 SWG to find out our results. We also have to decide what the highest current we will use will be; we have also done an experiment before for this. It shows that the current (I) is proportional to the voltage (v), this is ohms law.

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Conclusion

In our experiment we could have investigated a number of other things, such as the effect of cross sectional area or temperature on the resistance. If we had looked at the affect that the cross sectional area had on resistance we would probably find that as the wire doubled in cross sectional area the resistance would halve. This would be due to there being twice as many electrons so the current would travel a lot quicker and so decrease the resistance. If we looked at how temperature affected resistance we would probably find that as the temperature of the wire increases, the particles within begin to vibrate because they have so much energy, therefore it is much harder for the electrons to move through and so the resistance will rise. So instead of just investigating how length affected the resistance of a piece of wire we could also have investigated the affect of temperature or cross sectional area on the piece of wire.

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