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Investigating how the resistance of Nichrome wire depends on its length

Extracts from this document...

Introduction

GCSE PHYSICS COURSEWORK

INVESTIGATING HOW THE RESISTANCE OF NICHROME WIRE DEPENDS ON ITS LENGTH

A. PLAN

Introduction: My aim is to devise and experiment to measure the effect on resistance by changing the length of Nichrome wire.

Why Nichrome wire?

We have chosen Nichrome wire because it is able to produce a large resistance even with a relatively small area and is easily measurable, whereas suppose if we use copper wire then we will need a substantially large amount of wire for us to be able to measure the resistance.

What are current, voltage and resistance?

An electric current is a flow of negative electrons, and in our case the electric current flowing through the Nichrome wire, is measured in amperes (I). The voltage is the electric potential difference (PD) between two points (the voltage is the PD between these two points) and is measured in volts (V). Finally the resistance is defined as the amount of current flowing in the circuit for any set voltage applied to the circuit. It is measured in ohms (R). An equation linking current, voltage and resistance can be shown as; Resistance (R) = Voltage (V)/Current (I)

---------------------------------------------------------------------------------------------------------------------------------

What are the variables in the experiment?

i) Current – The current is the flow of the free electrons thought the Nichrome wire, which can flow though the whole wire if a voltage is applied across it. However, collisions occur with the electrons and the positively charged ions in the lattice and so the wire has shown resistance against the current as the movements of the electrons are being obstructed. Current in this experiment will be kept constant using an ammeter.

ii) Temperature (inside the wire)

...read more.

Middle

Start off the experiment by setting the crocodile clips apart by the start length. Length is measured accurately by measuring to the nearest centimeter (cm). Turn on the power supply and control it to make sure that the ammeter displays 0.8A, record the voltage shown by voltmeter. Turn off power supply, remove crocodile clips and replace on same length and repeat the previous steps three times. Do this for the rest of the measurements.

Preliminary results:

Safety:

  • When setting up apparatus make sure that the power supply is fully switched off.
  • Do not touch the Nichrome wire while the experiment is undergo as it may burn skin.
  • Do not turn the power supply too high, otherwise it could result in the fuse blowing.
  • While the experiment has commenced do not touch the crocodile clips as you could get a shock.
  • Make sure that the Nichrome wire is not so long that it makes contact with another object (e.g. a metallic pen).

Comments on preliminary results:

The results have helped me decide that 0.8A is a good current measurement to use in the real experiment because I get very little voltage variation. This will later ensure accuracy and precision. Also 0.8A is a good measurement because it is not too high current and so will not result in the wire increasing in temperature (due to more resistance).

B. OBTAINING EVIDENCE

Length (cm)

Current (A)

Voltage (V)

Average Voltage (V)

Resistance (Ω)

10

0.8

0.401

0.412

0.403

0.405

0.506

20

0.8

0.771

0.772

0.774

0.772

0.965

30

0.8

1.096

1.084

1.097

1.092

1.365

40

0.8

1.428

1.425

1.447

1.433

1.791

50

0.8

1.785

1.776

1.751

1.771

2.214

60

0.8

2.082

2.068

2.091

2.081

2.601

70

0.8

2.446

2.432

2.422

2.433

3.041

80

0.8

2.789

2.742

2.801

2.777

3.471

90

0.8

3.072

3.112

3.089

3.091

3.864

100

0.8

3.492

3.458

3.474

3.475

4.344

These are the results obtained from the experiment.

Please find enclosed on the following page, the graph to represent this data.

C. ANALYSIS

For the results I have recorded three repeats of voltage for each of the lengths and have rounded each numerical value to three significant figures.

...read more.

Conclusion

Reliability of conclusion:

The evidence which has been acquired is satisfying enough to support a firm conclusion. This is because the graph clearly showed a line which was directly proportional (as I predicted as well) and there were no anomalies to be found in any of the results. Even though I did get very minor errors before this has obviously shown very little. The graph has shown very little scatter and also I explained earlier how there is very little change in variation. However we cannot safely say that however, we do not have enough evidence to say whether length is directly proportional to length as this is just one experiment, so we need to do other experiments to confirm this theory.

        We can do further work and justify the experiment further by using more sophisticated equipment to ensure more accuracy for more reliable results. We could do other investigations such as; using a different thickness of wire and a different material of wire (to see if the same results apply to copper wire). We can also use a different current instead of 0.8A or actually use a larger wire with different measurements.

...read more.

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