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Investigating resistance.

Extracts from this document...


KS4 Coursework PHYSICS               2003-2005


Beth Davison

P                                                                        10A 1ss

O                                                                    Llandrindod Wells High School

A                                                                    Mr D.J. Lewis (P1)


Preliminary Work

                      An example of using the term resistance in every day language is to resist eating chocolate. This means to stop yourself from eating chocolate or to cut down the amount of chocolate eaten.

        According to “Usbourne Illustrated Dictionary of Science” resistance (R) is the ability of an object to resist the flow of current. The unit of resistance is ohm (      ). It also says that a resistor is a device with a particular resistance value, used to produce a required potential difference.

        Good conductors have low resistivity (the ability of a substance to resist current) and insulators have high resistivity.


              I predict that when I add more resistors in a parallel circuit the resistance will decrease because if I made two holes in the bottom of a bucket rather than one the water in the bucket would flow out twice as fast.

        I also predict that when I add more resistors in a series circuit the resistance will increase because if I walked down a short corridor and then I walked down a long one  it would take me a longer time to walk down a longer corridor. So, metaphorically, each time I add a resistor the “corridor” gets longer.


          1)A Series Circuit

                                                                with one resistor

                                                                with two resistors

  1. A Parallel  Circuit

                                                        with one resistor

                                                        with two resistors

...read more.


This is because as the cross section (thickness) of the wire increases then so do the number of particles (Q). If Q increases then so must I (the current) meaning that the resistance will be less. The graphs that I will produce from the results should look like this:

So as the cross section increases so do the number of charged particles but the resistance falls.

As the wires length is increased the time taken for the electricity to pass increases.

So, if the length of the wire doubles then the resistance would also double and the flow of electricity would half. Altering the wire is exactly the same as using a series circuit. You can see from my preliminary work that resistors in series circuits allow less current to pass through a circuit.

 An easy way to explain this is to use a corridor. If we made 30 people walk down a corridor 50 metres it would take them a certain amount of time, however if we then made the same people walk down a corridor 25metres long at the same speed then it would obviously take them longer. So by making the wire longer it gives the current further to travel so will take longer, just like the people in the corridor.

This can also be explained in the equation:

 I     =     Q  or                       Current    =   Number of charged particles

              T                                                                 Time

...read more.


        As I was doing the practical experiment I notices that the temperature of the length of wire in the experiment grew so that, if touched, it would burn someone badly.  To avoid this next time I would be faster and not leave the wire attached to the electric circuit whilst other things are adjusted with the apparatus.  I also think that next time I will use a power pack instead of singly battery cells.  Hopefully, by doing this, I would reduce the amount of resistance already in the circuit even before the experiment is started.  

I think that the evidence is very reliable and is completely sufficient to support my conclusion.  If I was to repeat this experiment I would try to find more evidence to support my conclusion.  I would change the material of the wire to see if resistance changes in different materials or whether it is just in length of cross-section that resistance changes.  Also, given more time, I would keep increasing the cross-section of the wire by twisting three, and then four, single wires together to see if the trend of resistance continues – which I would expect.  Also, as a precaution, I would use longer lengths of wire, not continue extending the length only by 10 cms  each time but more like 15-20 cm.  This would prevent the wire getting so hot.

...read more.

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