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Investigating how the length of a Wire affects its resistance.

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Introduction

By Logan Jayabalan 11Br Set 10.5

Investigating how the length of a Wire affects its resistance.

Aim : The aim of this investigation is to find out how the resistance of wire is affected by its length.

Hypothesis : I predict that when the length of a wire is increased, its resistance will also increase. I also think that the rate at which the resistance increases will be constant and directly proportional to the length.

References to books and the internet have been made to support the prediction:

“…However, the electron does not accelerate for ever. Eventually, it crashes into one of the atoms in the wire. Since atoms are far more massive than electrons, the electron loses all forward momentum every time it hits an atom (just as we would lose all forward momentum if we ran into a brick wall).. Immediately after the electron hits an atom its forward velocity is zero. The electron is then accelerated by [the battery]…” from the website:http://farside.ph.utexas.edu/~rfitzp/teaching/302l/lectures/node42.html

We can conclude from this that the longer the piece of wire is, the more chance there is of the electron colliding with other atoms. The more collisions that happen, the more resistive the piece of wire is. This text quoted from the science journal confirms this.

“Resistance is caused by electrons bumping into ions. If the length of the wire is doubled, the electrons bump into twice as many ions so there will be twice as much resistance. Soimage00.png

If the cross-sectional area of the wire doubles there will be twice as many ions and twice as many electrons bumping into them, but also twice as many electrons getting through twice as many gaps.

...read more.

Middle

Ammeter to check current

Voltmeter or Multimeter to check resistance

Ruler to check the length of the wire

Diagram

Circuit Diagram

The circuit will be set up as shown in the circuit diagram. This will be used for all the experiments, hopefully with exactly the same equipment.

        The experiment will be carried out whilst making all the factors that could possibly vary as static as possible. One such example of this is the temperature of the wire. This is a factor which has to be controlled externally, i.e. , it is not part of the circuit design and could be easily forgotten; it, however, can have quite an important bearing on the result obtained. For this reason, all the factors that could possibly vary whilst testing the circuit are kept as static as possible. This can be greatly helped by doing all of the experimentation in one go and using the same equipment throughout it.

Different equipment can lead to different results. This is because the resistance of the circuit can change when different equipment is used which can affect results. If the experiment is finished during a different time, conditions will have change, which could result in some independent variable factors that have not been considered, changing. This could adversely affect the reliability of my experiment

The resistance will be measured using a combination of an Ammeter and a Voltmeter. This is because the Ammeter is needed (as explained subsequently) for use in the circuit anyway. The resistance will be calculated using the equation V=IR which can be re-arranged to give

(Ecq4)    R=__V__

                         I

The variable resistor or rheostat will be added so that current in the circuit can be kept constant. This is essential because a longer wire (as hypothesised and theoretically proven before) should have a bigger resistance.

...read more.

Conclusion

        Undoubtedly, the best ‘improvement’ that could be made is to concentrate more on the setting up of the equipment and making sure that the length of the wire is exactly 20 cm (for example) by measuring 20 cm only from the inner edge of the crocodile clips. This will ensure that more accurate results are given.

        The alternative to this more rigorous checking would be use a higher current or smaller diameter of wire making the resistance higher which would lead to a larger range and better results due to less influence of small things such as not getting exactly 20cm of wire

        Further work that could be done would be to increase the voltage on the power pack from 4 volts to 6 or 8 volts and adjusting the current back down to 0.25A. This should give the same constant (or gradient of line on the graph); directly proportional results should also still be obtained. If this doesn’t happen, we know that there is something that is causing the results to not be the same. If we set up the equipment exactly the same each time, adjust the constant variables to the right levels and do basically everything the same, this different would either be because of human error or because of a constant variable we had not considered before.

© Logan Jayabalan 11 Brown 2002   -   OCR Triple Award Higher Physics 1982

Visit www.zenqua.netfirms.com for the website behind the person who wrote this (me)

...read more.

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