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Investigate how the electrical resistance of a wire changes in relation to its length.

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Introduction

Gabriella Blake
AIM: TO INVESTIGATE HOW THE ELECTRICAL RESISTANCE OF A WIRE CHANGES IN RELATION TO ITS LENGTH

PLAN

Introduction and background research
·     Resistance can be found using the equation
Resistance = voltage
current
·     It is measured in Ohms (Ώ)
·     Ohms Law states that the current (I) through a conductor is directly proportional to the voltage (V) across the conductor and inversely proportional to its resistance.
·     The resistance of a wire is effected by: -
Ø     Length
Ø     Diameter
Ø     Temperature
Ø     Type of metal
Ø     Cross-sectional area
·     In a conductor, some electrons break away from the atoms. These electrons move freely inside the conductor. When there is a voltage across a conductor, all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. Resistance is come across when the charged particles that make up the current collide with other fixed particles in the material. As the length of wire is increased, the number of collisions the current carrying charged particles makes increases and, therefore, the value for the resistance of the wire becomes higher.
·     In 1826, Georg Ohm discovered that the current flowing through metal wire is proportional to the potential difference across it (providing the temperature remains constant.) Georg Simon Ohm 1787-1854
·     An electric current is the flow of electrons (tiny negative particles)

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Middle


·     Type of wire- Some metals have less resistance than others. Using wires made from different metals would affect the resistance. The same wire will be used throughout the experiment to prevent this.




Accuracy
To make sure this experiment is accurate
·     The length of the wire must be measured precisely. It will be measured with a ruler to the nearest millimetre.
·     The wire must be completely straight during the experiment, to avoid short circuits. Bends and kinks in the wire could also affect the resistance.
·      The voltage reading must be taken as soon as the circuit is connected. This will minimalise the current’s effect on the temperature of the wire and thus the resistance.

Reliability
·     Each reading will be taken twice. Then both readings will be averaged to give the voltage. If two readings for the same wire length are very disparate, further readings will be taken to insure an accurate result.
·     To make the experiment reliable, all apparatus must be checked to see if it is functioning properly and is giving a true reading.
·     We will use the same apparatus throughout the experiment to make sure that nothing changes.
·     We will have the lengths all 5cm apart so that the results are not too similar and so it will be reliable.


Experiment
Apparatus
Ø     Nichrome wire
Ø     Rheostat
Ø     Power supply
Ø     Six connecting wires
Ø     Two crocodile clips
Ø     Voltmeter
Ø     Ammeter
Ø     Ruler




Method

1.
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Conclusion



Conclusion
My prediction was correct, the resistance was directly proportional to the length. This is because of the scientific idea, stated in the planning that if you double length, you double the number of atoms in it, so doubling the number of electron 'jumps', which causes resistance: The results support my predictions well, the results turned out the way I had expected, they match the predicted line well. I had predicted a straight line through the origin, which means resistance, is directly proportional to length. This also means that if the length was trebled or quadrupled the resistance would treble or quadruple. This is emphasised because the line of best fit is a straight line, which means the resistance is proportional to the length. This proves the fact that the longer the wire is, the more collisions there are between atoms and electrons. So if the wire increases in length, so does the resistance. If the wire decreases in length, so does the resistance.
Research
I got some information from GCSE textbooks but for my main source of information I used the search engines Google and Ask.

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