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A Resistance Investigation - Independent Variables

Extracts from this document...

Introduction

A Resistance Investigation

Independent Variables

These are variables, which we can change during the experiment to find out how they affect the electrical resistance of a length of wire.

  • The length of the wire
  • The diameter of the wire
  • The cross sectional area of the wire
  • The material the wire is made up of
  • The mass of the wire
  • The density
  • The temperature of the wire
  • Whether the wire is insulated or not
  • The configuration of the wire

Dependent Variables

For this experiment we are investigating the resistance of the wire.  The resistance cannot be measured directly, but it can be calculated

To calculate the resistance we will have to measure the

  • Potential difference across the wire
  • The current through the wire

Background Knowledge

An electrical circuit is the path of an electric current.  A current will flow through an electrical component only if there is a voltage or potential difference across its ends. The bigger the potential difference across a component the bigger the current that flows through it.  An electrical current is a flow of electrons. The electrons flow from the atom to atom in a piece of wire. The flow of the electron current leaves positively charged ions, which vibrate with in their fixed position.        

A series circuit is were all the components are connected together in a loop and the entire current flows threw each component in the circuit. The total potential difference is equal to the potential difference in each of the components in the circuit.

A diagram of a Series Circuit

In a parallel circuit the components are connected separately they are arranged to allow all positive (+)

...read more.

Middle

Power source

Length of wire (cm)

Volts (V)

Amps (A)

Battery

200.0

3.65

0.81

5.0

1.02

2.08

15.0

0.47

0.97

100.0

0.95

0.29

180.0

1.5

0.25

20.0

80

1.24

Cell

100.0

60

0.18

200.0

60

0.09

20.0

60

0.81

60.0

60

0.31

Conclusions

The preliminary trials were successful we achieved all our objectives. For the power source we decided to use a cell because the voltage was much easier to control because its maximum potential difference is a lot smaller than that of a battery, and we found it hard to keep at a constant voltage suitable for all lengths of wire. Now that we had decided on the apparatus the circuit diagram could be completed and finalised. Our predetermined voltage is 0.60V the current remain under one amp for all lengths of wire. We final concluded that we would take our readings from 20cm of wire to 200cm of wire and record the current at 20cm intervals.

Safety

To ensure that this experiment is safe I will be making sure I

  1. Use a switch and disconnect the circuit when I am changing the length of the wire.
  2. Avoid unnecessary path of undesired current creating a short circuit.
  3. I will keep water away from the apparatus so there is no possibility of creating a short circuit which may also to significant heat being produced
  4. I will keep the current below one amp because if it goes above one amp the circuit will heat up significantly and there will be a chance of burns from the specimen wire.

Apparatus

Apparatus

Measure of accuracy

Connecting Wires

Voltmeter

0.01 volts

Ammeter

0.01 amps

Crocodile connecting clips

Switch

Length of wire

A 2 metre specimen of constantan

Rheostat

Ruler

1 millimetre

Cell

1.5V

Method

  1. Measure the length of the wire with a ruler
  2. Set up the circuit as in the diagram
  3. Place the length of wire in the circuit
...read more.

Conclusion

Improvements

Our investigation could have been improved; these are the ways that I think it could have been done to improve the reliability of the evidence.

  • We could have used a ridged ruler of more than 2 meters, so there would be no inaccuracies with the measurements.
  • If we had a straight piece of wire then that also would have made the measurements more accurate.
  • If we had a wider range of results, e.g. measure the resistance at 10cm intervals along the wire.
  • We could have taken more repeat readings to increase the reliably of the results.
  • We also could have used a data logger, which would have recorded the ammeter and voltmeter and plots the graph automatically; if this was done then we could use it for an even wider range of results, increasing the accuracy of the experiment even more.

Further Work

This investigation could be extended to give more accurate and meaningful results and to see what other factor could influence a change in resistance. Here are some other factors that can be investigated.

  1. Increase the length we measured beyond 2 metres, but keep the voltage, material, temperature and the diameter the same.
  2. Change the material of the wire but keep the lengths and voltage, temperature and diameter constant.
  3. Change the voltage but keep the material of the wire, the diameter, temperature and the lengths the same.
  4. Change the environmental temperature, but keep the material, diameter, lengths and voltage the same.
  5. Change the diameter of the wire but keep the material, voltage, temperature and lengths the same.

All of these different experiments would help the comparison and help further investigate what factors affect resistance.

...read more.

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