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# Investigate how the resistance of a wire is affected by the length of the wire.

Extracts from this document...

Introduction

Tom Levick

AT1

## GCSE Physics Coursework - Resistance of a Wire

My aim of this investigation is to;

To investigate how the resistance of a wire is affected by the length of the wire.

What is resistance?

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat. In metals, not only do the atoms vibrate more when heated, but the free electrons charge around more as well. These transfer the energy much faster than just vibrations in bonds.

How is it measured?

The resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and the voltage across the wire (in parallel). These measurements are then applied to this formula:

Middle

Part O obtaining evidence

Below are two tables detailing my experiment’s results. The first table is the first run, and the second is the repeats table. The final table is the average resistance for each length I tested at.

 Length of wire (cm) Voltage (volts) Current (amperes) Resistance (Ω) 100 3.4 0.3 11.33 90 3.35 0.325 10.3 80 3.3 0.35 9.4 70 3.3 0.4 8.25 60 3.25 0.48 6.77 50 3.2 0.55 5.82 40 3.15 0.7 4.5 30 3.1 0.9 3.44 20 2.9 1.4 2.07 10 2.6 2+ 1.3 0 0 2+ 0

Conclusion

For a particular result, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then. If it is higher than it should be then the connections could be cleaned. Whilst extremely unlikely, it is conceivable that the power supply was providing a different voltage for some of the results. This is unlikely to be a problem in this investigation but it might have been an issue had we used batteries instead.

NB:      If one were to assume that Ohm’s Law applies, then another possible explanation could be that at some points (more likely in the lower lengths), the wire was not allowed to cool completely so that the temperature was higher for that measurement. Whilst unlikely (due to the two sets of results), this would cause a higher resistance as explained previously.

For further work one could change this by maintaining the temperature of the wire at a constant temperature throughout each experiment I could do this by submerging the wire in a cold substance for example refrigerated fire resistant gel. Also one could eliminate the areas of Human error by using a computer to measure and record the results and also maintain quality control in the form of a fairer test. I could also eliminate the stretching go the wire by using a new piece each time I collect my results.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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