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# Investigate if the length and cross-sectional area affects resistance through a circuit.

Extracts from this document...

Introduction

PLAN FOR SCIENCE INVESTIGATION

## Aim:

My aim is to investigate if the length and cross-sectional area affects resistance through a circuit.

## Back ground scientific knowledge

What resistance is:

## To find the resistance of something we use the following formula:  V

Resistance = V                                                    I    R

#### I

Resistance is the ratio of potential difference.

As long as I × V and the resistance is constant, and the conductor obeys Ohms Law.  The voltage increases, as long as they increase at the same rate.

V

Constant

Temperature

I

Ohm’s law

Ohm’s law means that if the voltage is doubled, the current will be doubled. The formula for ohm’s law is the following:

V = I × R

This defines resistance, for Ohmic conductors the resistance is constant, and ohm’s law of proportionality holds.

What causes resistance is:

Resistance of a straight wire depends on:

1. It’s length- the resistance increases with the increasing length.
2. It’s thickness- the resistance is greater for thinner wires.
3. It’s material- good conductors have a lower resistance.

Middle

= Atoms vibrating

Electrons move around the lattice in a random movement, with different speeds and different directions.  They collide with each

Other and the atoms. As they hit into each other the movement is passed on and the vibration increases.  More collisions mean greater resistance and more energy exchange.

Variables

Length: The longer the piece of wire the more collisions there is, and therefore the greater the resistance for a given current.

Cross-sectional area: The narrower the conductor the greater the number of collisions for a given current.

Temperature: the higher the temperature the more vibration in the lattice, the more collisions for a given current.

Material: the material from which the wire is made.

Resistively: resistively is related to the number of factors, which

affect resistance:

• Number of free electrons
• Crystallinity in lattice

By reducing crystallinity, it quickens up the flow of electrons and increases collisions, for a given current.

Preliminary work

To help me understand more I have decided to do some preliminary work.  This will help me to research the experiment and explore faults in the experiment.

Conclusion

Conclusion

My graphs show that there is a relationship between my voltage and current.  I can see that my results form a straight-line graph, which shows that my results are correct. I can also say that my choice of equipment was correct as I obtained good results. I controlled the variables well throughout the experiment, particularly the temperature.  I did this by switching off the D.C power supply after each result, to keep the temperature down.  I have discovered that the smaller the CSA of the constantan wires, the lower the resistance. I have observed the relationship between voltage, current, and gradient.  The higher the gradient the greater the resistance, which means there must be an increasing voltage and current.  My graph shows that it obeys ohms law, and did not over heat.  Overall it showed to be a success because I obtained a straight-line graph.

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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