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To devise an experiment to investigate on how the resistance of nichrome wire depends on its length

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Introduction

Physics practical coursework

PLANNING

Aim: To devise an experiment to investigate on how the resistance of nichrome wire depends on its length.

Introduction

In this physics practical coursework I will be “Investigating how the resistance of Nichrome wire depends on its length.” We will be investigating via an experiment carried out in class using the apparatus available to us. We know that electrical resistances arise when there are collisions between electrons and the ions (positive cations), and we will be trying to prove this, by this experiment. The nichrome wire which we will be using will be 24 S.W.G. (standard wire gage). We will basically keep the current the same throughout the experiment, and measure the variations in voltage as the length of the wire is increased or decreased.

The Variables    

The variables for this experiment are:

-Temperature

-Cross sectional area

-Current in the wire

-Length of wire

-Diameter of wire

-Type of wire

We are investigating the effects of changing the length of wire, and so only this variable will be changed and experimented on! All other variables will be controlled and kept constant throughout the whole experiment.

How to make experiment a fair test

Since we are investigating the effects of changing the length of wire, only this variable will be changed and experimented on!

...read more.

Middle

Quantative theory: We can explain this scientific theory using quantative theory; when a length of 10cm is used, the resistivity of a 20cm length of wire would be doubled, because there would be twice the number of collisions between the electrons and ions and therefore twice the resistance. Similarly when a 60cm wire is used we would expect the resistance to be thrice the resistance of 20cm length because there will be three times the number of collisions between the electrons and ions in comparison to the 20cm length.

Ohms Law

For many materials particularly metals if the temperature is constant then the current flowing is directly proportional to the voltage, i.e. the resistance is constant. Ohms law states that if the cross section of the wire is uniform then the resistance is proportional to the length and inversely proportional to the area of the cross section.

Apparatus

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Pictorial view of experiment

Circuit diagram

Method

  1. Collect all apparatus stated above.
  2. Place meter length of nichrome wire as straight as possible, on the ruler and stick it with tape.
  3. Obtain the ammeter, power supply, and the wires for the circuit.
  4. Plug the power supply in, however don’t turn it on.
  5. Complete the circuit, including the power supply, the nichrome wire, and ammeter in series.
...read more.

Conclusion

The nichrome wire which is stuck onto the ruler should be handled with care, as it will be sharp at the ends.Crocodile clips should be handled with care too.A voltage which is too high from the power supply could also potentially damage the ammeter.

Accurate determination of length

Despite the fact that we only had a meter rule to measure the length of the nichrome wire, we still had to ensure that we could get the lengths as accurate as possible. It was very hard to get the nichrome wire straight as it had bends and bumps in it. We did not have any device to pull the wire and straighten it. Therefore the actual length of the wire was a bit longer than one meter as it wasn’t straight and the bends made the length longer. In order to keep the length of the wire as accurate as possible, we straightened the wire, and stretched it manually and stuck it onto a meter rule with sticky tape.

The metre rule was accurate to the nearest centimetre; however we didn’t really need it to be any more accurate. If a more accurate experiment were to be done with more precise measurements, then maybe more accurate measuring equipment would be needed.

...read more.

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