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How the Resistance of a Wire is affected by Cross-Sectional Area

Extracts from this document...

Introduction

How the Resistance of a Wire is affected by Cross-Sectional Area.

Introduction

Resistance is the opposition a component has on the flow of current and it is measured in Ohms. Resistance occurs as the electrons move along the wire they collide with the metal atoms. These collisions make the atoms vibrate more, which make the metal hotter, they also slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is for the electrons to move through the wire.

There are four factors that affect resistance in a wire.

They are:

1. Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as, the atoms are moving into the way of the electrons. This increase in collisions means that the resistance of the wire will also increase.

2. Material: The type of material will affect the amount of free electrons which are able to flow through the wire, if the material has very few atoms then there will be high number of electrons causing a lower resistance because the electrons would have less collisions making it easier for the current to flow.

...read more.

Middle

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Safety

I have decided to take some safety precautions by Keeping the voltage at 3 volts because 4 is dangerous, being careful when connecting the wires and while handling the live subject wire.

I also wore goggles and used heat proof mats to prevent the live wire from burning the table.

Method

  1. Firstly I am going to connect the voltmeter to the Power supply.
  2. Connect up all the wires.
  3. Connect the ammeter.
  4. Use crocodile clips to connect the subject wire.
  5. Turn the power supply on to 3 volts.
  6. The circuit should look like my diagram in the aim.
  7. Write down the readings on the ammeter and voltmeter.
  8. Repeat for all the thicknesses of wire.
  9. After all the wires have been done create a table and calculate the resistance of each wire.
  10. Lastly repeat all steps 2 times for reliable results.
  11. And find the averages for the results you have collected.

Preliminary Work

I have decided to use 20 cm of wire as it seemed a sensible length.

I also determined to use 3 volts, because 4 volts melted the wire, and 3 seemed a reasonable, safer alternative. I experimented on which of the two materials to use. (Nichrome or Constantan).

I compared results on two different thickness SWG 32 and SWG 26 and recorded this information in three tables and three graphs.

In conclusion I have decided to use Nichrome wire to experiment on because it has a greater resistance and larger range between highest and lowest resistance.

By using nichrome my results are likely to be more reliable and easier to see how resistance increases as cross-sectional area decreases.

Actual Experiment

I will perform my actual experiment using the method below and considering the safety measures necessary

Apparatus list:

  • Power Supply – used to supply an electrical current and voltage
  • An Ammeter- used to measure current in amps, connected in series.
  • A Voltmeter- used to measure voltage. Connected in parallel.
  • Four different thicknesses of Nichrome wire- used to experiment on.
  • Meter ruler- used to keep the wire to 20 cm long.
  • 2 crocodile clips- used to connect the subject wire to the circuit.
  • Connecting wires- to connect all the components.
...read more.

Conclusion

Results for Re-Experiment to Follow (at end of Evaluation)

To improve accuracy I could also consider an alternative method for the experiment the method follows:

Method

 1. Firstly I am going to connect the voltmeter to the Power supply.

 2. Connect up all the wires.

 3. Connect the ammeter.

 4. Use crocodile clips to connect the subject wire.

 5. Turn the power supply on to 3 volts.

 6. The circuit should look like my diagram.

image00.png

 7. Write down the readings on the ammeter and voltmeter.

 8.  Repeat for all the thicknesses of wire.

 9.  After all the wires have been done create a table and calculate the resistance of each wire.

10.  Allow wire to cool before continuing to the next stage.

 11.  Lastly repeat all steps 3 times for reliable results.

 12.  And find the averages for the results you have collected.

As I am aware that heat affects the accuracy of the results I have added a stage to allow the wire too cool, therefore reducing the possibility of an error

...read more.

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