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# The aim of our investigations is to find out the ohmic limit so I can determine what current I should use in the actual experiment.

Extracts from this document...

Introduction

Vivian Okrah

Candidate: 9428

Resistance of a wire

Preliminary Work

Aim:

The aim of our investigations is to find out the ohmic limit so I can determine what current I should use in the actual experiment.

Plan:

I will use three different currents which will be 0.2A, O.3A and 0.5A, then measure the voltage across the different lengths of wire they are 20cm, 40cm, 60cm, 80cm, and 100cm. This will be done for each current. We will have to vary the length of the wire so the results will be diverse and will also make it easier to produce a graph representing the results  we will use three different current to obtain a reliable ohmic limit. I will then record my results in tables and produce of graph that will show me the ohmic limit. The power pack will be placed on 2V, so the current will be kept at a constant rate.

Method:

Firstly I will collect up equipment and set it up as shown in the diagram. I will then set the voltage on the power pack to 3v, and place a 10cm length of nichrome wire between the two distances.

Following this I will use the voltmeter to read the voltage across this length then use the ammeter to read the current flowing through this length to check if it is correct.

I will then record my results on a table and repeat these steps for the rest of the lengths, increasing the length 20cm every time.

Tables:

 Length (cm) Current (A) Voltage (V) 20 0.2 0.5 40 0.2 1.0 60 0.2 1.5 80 0.2 1.5 100 0.2 1.6
 Length (cm) Current (A) Voltage (V) 20 0.3 1.5 40 0.3 2.2 60 0.3 3.0 80 0.3 3.3 100 0.3 3.5
 Length (cm) Current (A) Voltage (V) 20 0.5 0.7 40 0.5 1.2 60 0.5 2.0 80 0.5 2.7 100 0.5 3.2

Obtaining Evidence

 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 10 0.2 0.7 3.5 3.4 10 0.2 0.6 3 3.4 10 0.2 0.6 3 3.4 10 0.2 0.8 4 3.4 10 0.2 0.7 3.5 3.4
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 20 0.2 1.5 7.5 7.4 20 0.2 1.4 7 7.4 20 0.2 1.5 7.5 7.4 20 0.2 1.5 7.5 7.4 20 0.2 1.5 7.5 7.4
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 30 0.2 2.0 10 9.7 30 0.2 2.0 10 9.7 30 0.2 1.9 9.5 9.7 30 0.2 1.9 9.5 9.7 30 0.2 1.9 9.5 9.7

Middle

Length of wire (cm)

Current

(amps)

Voltage (V)

Resistance (Ω)

Average Resistance (Ω)

50

0.2

2.6

13

13

50

0.2

2.6

13

13

50

0.2

2.6

13

13

50

0.2

2.6

13

13

50

0.2

2.6

13

13

 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 60 0.2 2.9 14.5 14.9 60 0.2 3.0 15 14.9 60 0.2 3.0 15 14.9 60 0.2 3.0 15 14.9 60 0.2 3.0 15 14.9
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 70 0.2 3.2 16 15.6 70 0.2 3.1 15.5 15.6 70 0.2 3.1 15.5 15.6 70 0.2 3.1 15.5 15.6 70 0.2 3.1 15.5 15.6
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 80 0.2 3.2 16 16.8 80 0.2 3.3 16.5 16.8 80 0.2 3.5 17.5 16.8 80 0.2 3.4 17 16.8 80 0.2 3.4 17 16.8
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 90 0.2 3.5 17.5 17.5 90 0.2 3.5 17.5 17.5 90 0.2 3.5 17.5 17.5 90 0.2 3.5 17.5 17.5 90 0.2 3.5 17.5 17.5
 Length of wire (cm) Current(amps) Voltage (V) Resistance (Ω) Average Resistance (Ω) 100 0.2 3.6 18 18 100 0.2 3.6 18 18 100 0.2 3.6 18 18 100 0.2 3.6 18 18 100 0.2 3.6 18 18

## Analysis

Using the data I obtained from my experiment I was able to calculate the average resistance for each length, and then plot these averages on a line graph.

From analysing my graph, I can see that there is a pattern. Some of the results I recorded from my experiment correspond with my one of my hypothesis, in the beginning of my coursework, which states that the resistance of the wire will increase as the length of the wire increases. But on the other hand it goes against my second hypothesis which states that doubling the length of the wire will double the resistance, this relates back to Ohm’s law, which says that in electricity, the fact that the amount of steady current through a large number of materials is directly proportional to the voltage across the materials and inversely proportional to the resistance to the current. My graph shows characteristics of being a non-ohmic conductor.

Conclusion

The reasons these problems may have occurred are as follows:

• The power pack may have been left off over a long period of time which allows the Nichrome wire the to cool down causing the wire to have less resistance and therefore leading to anomaly results.
• Perhaps it could have been that the crocodile clips that were attached to the wire may have slipped and become lose therefore not increases the voltage as much as it should be.
• The length that was measured for that particular distance was incorrect. It is possible that the length was shorter, causing a lower resistance and at a majority of the lengths it is possible that it was causing a higher resistance also leading to anomalous results.

We also encountered many difficulties whilst carrying out the experiment such as placing the wire in the 5v hole and then reading the voltage off the line that went up to 15v instead of 5v. So we had to repeat the experiment in order to keep it a fair test.

To avoid these errors in the future I would make sure the power pack would stay on for the same amount off time for each length I would do this by timing it.

An alternative way of doing the investigation would be to use a data logging system which involves digital voltmeter and ammeter and use wire with a larger diameter therefore the clips will not come off easily. I think this would have gave me a more reliable set of results and it would also be a more efficient way of doing the experiment because more time would be saved.

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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