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# Wire Resistence Practical

Extracts from this document...

Introduction

Physics Assessed Practical

James Highmore

Planning

Resistance slows the current in a circuit. The formula is as follows:

 R = V I

This means that:

 Resistance = Potential Difference Current

Therefore, to calculate resistance, the potential difference and current need to be known. Potential difference is measured in Volts with a Voltmeter. Current is measured in Amperes (or Amps as they are more commonly known) with an Ammeter. Resistance is measured in Ohms (Ω).

 -    Electron -        Atom

At atomic level, resistance is the action of atoms vibrating in the wire, blocking the flow of electrons. In effect, resistance is a “bottleneck”. The diagram below illustrates this:

On their journey, the electrons do not have a clear path because of the atoms in the way. This slows them down.

I predict that as the length of the wire increases, so does the resistance. This is because, as the length of wire increases, the number of atoms in the wire will increase too. This means that the electrons’ route will be obstructed even more.

Middle

 Length of wire (cm) Current (A) Voltage (V) Resistance (Ω) 10 0.2 0.3 1.50 0.6 0.8 1.33 20 0.2 0.4 2.00 0.6 1.2 2.00 30 0.2 0.6 3.00 0.6 1.7 2.83 40 0.2 0.8 4.00 0.6 2.1 3.50 50 0.2 0.9 4.50 0.6 2.7 4.50 60 0.2 1.0 5.00 0.6 3.2 5.33 70 0.2 1.2 6.00 0.6 3.6 6.00 80 0.2 1.5 7.50 0.6 Voltmeter reading off scale - 90 0.2 1.5 7.50 0.6 Voltmeter reading off scale - 100 0.2 1.7 8.50 0.6 Voltmeter reading off scale -

It was shown after the experiment that:

• When the current was at 0.2A, the results were not accurate enough to draw proper conclusions.
• When the current was at 0.6A, the Voltage readings for 80cm and over were too high to be shown on the Voltmeter.

The graphs for the 0.2A and 0.6A results are located on the next page.

Obtaining and Presenting Evidence

I chose to keep the current a constant of 0.

Conclusion

On the subject of the wire, the crocodile clips were not very accurate when being placed every 10 centimetres. A more accurate appliance to use could have been, for example, a knife or needle. This is because these objects have a smaller surface area and so could be more accurately placed where they needed to be placed.

Another major problem in the experiment was that there was approximately 0.5Ω in the circuit before any extra resistance was added. This resistance may have been from components already in the circuit, or the connections between them. To reduce resistance in connections, higher quality ones could be used. Ideally, gold connections would be the best, but a cheaper alternative would be brass.

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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