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Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire.

Extracts from this document...

Introduction

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Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire.
These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how
hard it is to move the electrons through the wire.

Resistance is measured in Ohms. This was the scientist who discovered resistance.  Ohm created a law, and called it Ohm’s Law.

“Ohm's Law deals with the relationship between voltage and current in a metallic conductor.”

This relationship states that

“The potential difference (voltage) across an ideal conductor is proportional to the current through it.”

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Current (I): is the result of electrical charges on the move. This charge is more than often carried by the negative electrons.  For the current to flow there must be a continuous pathway between the terminals of the power supply. Current is calculated using a device called a Ammeter and is measured in amperes (A)

Voltage (V) (also known a Potential Difference. p.d)

The Potential Difference is the energy transferred to other forms per unit charge. So, in a series circuit the voltage (p.d) may be found by adding the voltage across the separate components e.g. bulbs. Voltage is calculated using a device called a Voltmeter.

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Middle

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I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to
collide with the atoms. So if the length is doubled the resistance should also double.

This can easily be shown in everyday life. If you have a long corridor there is more chance of less people colliding than in a very small corridor.

We will be keeping everything in the experiment the same the whole way through (battery pack, voltmeter, ammeter, wires etc.) however the only thing we will change is the length of wire being tested. This is done so the test is a ‘fair test’ and there is no bias involved.

Once I have preformed my experiment I will use graphs and tables to try and see if my prediction was correct.


Points of Safety

  • Always avoid switching on/off the power supply with wet hands.
  • Allow the wire to cool in-between experiments.  
  • Ensure the power supply is switched off before you make any alterations to the circuit.
  • In an emergency, use the on/off switch on the power supply its self to break the circuit.
  • Do not leave the circuit unattended when the power supply is switched on.
  • Do not leave the power supply on for long lengths of time.

Fair Test Points

  • Make sure that the voltage coming from the power supply is kept constant throughout the experiment.
  • Maintain the same current (0.3A) throughout the experiment.
  • Use the same wire to prevent unwanted variations, for example altering width or density.
  • Repeat the experiments and find the average to obtain more accurate results.
  • Use mounted bulldog clips to give the experiment a secure and static base, and to prevent unwanted movement
  • Switch off the power supply and allow the wire to cool in-between experiments, to prevent any initial resistance.
  • Use the same equipment, particularly the same ammeter and voltmeter, as others don’t always share the same resistance.
  • Make sure all experiments are carried out under the same temperature conditions, for example on the same day, as an increase in temperature, increases resistance.
  • Add an extra 1cm onto the length of the wire to ensure that there is 0.5cm on each end for the bulldog clips to sit. This reduces error.
  • Use a current of 0.3A, as this will cause minimal heat and resistance to the wire.
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Conclusion

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My results are not completely accurate for many reasons:

The temperature of the wire will rise which will affect the resistance. The temperature will increase because when there is a current flowing through a resistance, this will cause the atoms in the wire to vibrate, stopping the flow of electrons therefore the resistance will increase. I could of over came this by putting the wire in a beaker of cold water.

When measuring the lengths of the wire the length might not be accurate as the wire might not be completely straight.

There could have been a different thickness in the length of wire.

Even though of all these problems my results are still accurate enough to support my prediction. If I did this experiment again, I would use newer, with a more sensitive range ammeters and voltmeters, a more accurate way of measuring, and I would take a wider range of readings, and more readings so I could get a more accurate average. I would also investigate other factors such as, temperature, voltage and type of wire, to see how these affect the resistance.


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To help me with this investigation I used the following:

Complete Physics by Stephen Dople

Letts GCSE Physics

CGP Physics by Richard Parsons

Encyclopaedia – Britannica 99 CD-Rom

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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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