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Investigating the Resistance of a Wire.

Extracts from this document...

Introduction

Physics Coursework

Investigating the Resistance of a Wire

In this piece of coursework I am going to investigate the resistance of a wire.  This will be done by performing experiments testing the wire under different conditions to see whether they affect the resistance.  Knowledge I already have to help me complete this experiment is Ohms Law and how to measure resistance using a voltmeter and an ammeter.

Ohms Law was created by Georg Ohm who set out to find a relationship between the current through a wire and the voltage between its ends in the 1820s.  After testing different lengths, thicknesses, metals and even different temperatures, Ohm established a law which states ‘The current flowing through a metal wire is proportional to the potential difference across it, providing the temperature remains constant.’  This can be expressed as the formula V = I x R.

  • V is the symbol for potential difference (voltage) and is measured in volts, V.  It is the driving force that pushes the current around a circuit.
  • I is the symbol for current and it is measured in amperes, A.  Current is the flow of electrons around the circuit.
  • R is the symbol for resistance and is measured in ohms, Ω.  Resistance is anything in the circuit which slows the flow down.  It opposes the flow of the electrons.

However for this experiment I will rearrange this formula to suit my purpose of finding resistance.  The formula I will use will be:

Resistance = Potential Difference

                                                       Current

Ohms law has helped the design of telegraph lines, motors, power lines and nearly the whole development of electrical equipment through the last century and this century so it is very important to investigate.

Variables

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Middle

The voltmeter measures the voltage across my test object and is measured in volts.  In a circuit the voltmeter is always connected in parallel with the test object as it needs to measure the voltage across it.  The voltmeter will give me a reading for the potential difference which will allow me to work out the resistance of the wire.

The ammeter measures the current flowing around the circuit in amperes (amps). Unlike the voltmeter the ammeter is connected in series and will allow me with the voltmeter reading to work out the resistance.

Other apparatus used in this experiment will include:

  • A meter ruler – to measure the length and diameter of the wire.
  • Crocodile clips – to connect the test wire into the circuit.
  • And various other wires to connect the above items together and complete the circuit.

Method

I will set up the apparatus from the previous page in the circuit I have explained.  The wire I am testing will be attached to the meter ruler.  The positive crocodile clip will be attached at 0cm and the negative clip is moved up and down the wire stopping at the measurements I will take.  I will measure the resistance of five different lengths and five different diameters of the constantan using the reading from the ammeter and voltmeter.  I will measure the current going through the wire and the voltage going across the wire for each length and diameter.  I will then find the resistance of each different length and diameter I will measure using Ohms Law; R = V/I.  I will repeat the process for each length and diameter I will test three times to prevent any errors occurring.

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Conclusion

  • Black Putty – my test object which can molded in to the different lengths and diameters I will test.
  • Power supply – kept at a constant 3 volts to ensure my results are as accurate as possible
  • Crocodile clips – to connect the black putty being investigated to the rest of the circuit.
  • Voltmeter – to measure the potential difference and help me to figure out the resistance of the putty.
  • Ammeter – to measure the current and help with the potential difference to figure out the resistance of the putty.
  • Variable resistor – to allow the current to be changed
  • Wires – to connect the above items together and complete the following circuit.

For Experiment 1, investigating the connection between length and resistance I will firstly set up the apparatus I have just explained.

I will measure four different lengths of putty; 15cm long, 10cm long, 5cm long and 2.5cm long, keeping the diameter of the putty at a constant 1cm thick.

I will note down the voltage and current in the following tables and use these readings to help me work out the resistance.

This experiment will be repeated three times to give me an average resistance, which will be more accurate as errors are limited.

Experiment 2 will investigate the relationship between diameter and resistance.  

The circuit will be set up the same and the experiment will be repeated three times just as in experiment 1.

However I will use the following diameter measurements and keep the length a constant 8cm: 1cm thick, 1.5cm thick, 2cm thick and 2.5 cm thick.

The following tables show the results of my experiments.

Conclusion

My results show that as the length of the black putty decreases the resistance also decreases.  When the diameter of the black putty increases the resistance decreases.  This conclusion will help me with my plan and predictions and prepare me for my main experiments.

Rosanna Sherrard  11G

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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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