# The Change in Resistance of a Carbon Paper

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The Change in Resistance of a Carbon Paper

Introduction

The aim of this experiment is to see how the resistance of a carbon-coated piece of paper changes when the different variables change.

Variables

A variable is a change in an experiment that could alter the outcome/results of that experiment, and for this experiment the main variables are type of paper, width of paper, length of paper, and temperature.

We are going to be studying how changing the width of the paper affects the resistance, and so to ensure a fair test we will have to keep all of the other variables constant, as if they were also changing the results could be affected and the experiment would not be of any
Preliminary Experiment

The purpose of the preliminary experiment was to decide on an appropriate length to keep the paper constant at, and an appropriate shunt for the ammeter. The layout and format is the same as the main experiment (see later).

We tested the various ammeter shunts, and decided to use the 10mA shunt, as it gave a reading in the middle of the scale, whereas the other shunts had given readings off or almost off the scale.

We also found that 32.5cm was the optimum length for the paper, as it puts the reading at about 10 on the scale, which is a good as it ensures that as we decrease the width (hence decreasing the amperes), the readomg will not go off the scale as it was high to start with- if we had started with a length that put it at something lower like 3 to start with, it could have gone off the bottom of the scale and we would have to start over.

Apparatus

-Electric wires

-Ammeter (and shunt)

-Voltmeter

-Carbon-coated paper

-Scissors

-Ruler

-Cyclon cell

-Clips

Diagram

The diagram below shows how we will set up the apparatus, in a standard circuit diagram.

The clips are clipped onto both ends of the carbon-coated paper, and so the current can flow through it. The width of the paper will start at 7cm, the length at 32.5cm,