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GCSE Science - Resistance on a wire

Extracts from this document...

Introduction

        Science Resistance in a Wire

GCSE Coursework

Science

Resistance in a Wire

Chantal du Thoit

Candidate number: 0002

15/02/2006


Table of Contents

1)Introduction

Factors that affect the electrical resistance of a length of wire

Apparatus that I’m going to use.

Preliminary work

2)Hypothesis

3)Method

4)Results

5)Evaluation

6)Conclusion


  1. Introduction

An electric current flows when charged particles (called electrons) move through a conductor. As the electrons move through the conductor they collide with the conductor’s atoms. This makes it more difficult for the current to flow which is what we know as resistance.

George Ohm discovered that the emf (electromotive force) of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one (i.e. the current or voltage) you also triple the other.

He also discovered that a circuit sometimes resisted the flow of electricity. He called this resistance. He then came up with a rule for working out the resistance of a circuit:

V/I = R or image00.png

V - Volts
I - Current
R - Resistance


Factors that affect the electrical resistance of a length of wire

There are three main factors which affect the resistance of a wire: the material of the wire (what the wire is made out of)

...read more.

Middle

At 50cm

0.18

0.5

2.8

At 20cm

0.18

0.2

1.1

Copper:

At 100cm

0.18

0.01

0.1

At 50cm

0.18

0.01

0.1

At 20cm

0.18

0.01

0.1


All figures are rounded to 1 decimal place.

After obtaining these results I decided to use a nichrome wire in the actual experiment. Although it has the highest resistance it’s the only wire that didn’t go below 1 ohm at 20 cm. and therefore should be the easiest to obtain measurable results in the shorter lengths of wire.


  1. Hypothesis

Using Ohm’s law I predicted that as the voltage decreases there will be less resistance. I predicted this because if the current had stayed fixed, then reducing the voltage would automatically reduce the resistance in the Ohm’s Law formula.

If there is a high voltage there will be a high resistance. With a low voltage there will be a low resistance.

I also predicted that the resistance would decrease depending on the length of the wire (the longer the wire the higher the resistance).




  1. Method

Before performing the tests I wrote down what I should keep the same in order to make it fair, which were: the type and diameter of the wire (by using a single length of nichrome wire); the length of the wire (by accurate measuring and moving the crocodile clips)

...read more.

Conclusion

They weren’t exactly the same but this could have been for a variety of different reasons. For example, as I’ve already said, the wire may have become too hot which would affect the resistance as the current flows faster with heat and therefore the resistance would have increased.

If I did the experiment again I would leave the power pack turned off for longer in between taking each reading so I could be absolutely sure that heat did not affect the results.

I would also make the wire longer to see if there was any noticeable difference in a wire longer than 100cm.

If this test was repeated by someone else they would obtain results similar to mine. They wouldn’t be exactly the same, however, as it depends how they are reading the scale and whether the equipment is set up correctly etc.

To further test my predictions I would do the experiment on other wires and not just on nichrome. I would use the copper, iron, steel and/or brass wires.

If someone did all of this, their results may lie even closer to the line of best fit on a graph.

  1. Conclusion

From my results you can see that my hypothesis was correct.  I found out that as you increased the length of wire, the resistance also increased.

...read more.

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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