An experiment to find the Resistivity of Pencil leads in different degree of hardness

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An experiment to find the Resistivity of Pencil leads in different degree of hardness

Introduction:

A lead pencil, is not really made of lead, instead, it is made from graphite, which is a form of carbon. Carbon is one of a class of substances that will conduct electricity, like a conductor, but will also block some current.

(the parameter in about why under what circumstances it does not conduct)

Aim:

The aim of this experiment is to find out the resistivity with different hardness of graphite (pencil leads, which relates to quantity of carbon in the lead). To measure the resistance of the lead, the ohm’s law equation will be used R= V/I (despite heat having been produced)

  , then

Using the equation: A (Cross-sectional area) R (resistance)/ L (Length) =ρ (Resistivity)

ρ=    A R    

        L

Preliminary Work:

In order to find out the range of voltage to be used, the following data shows the result from the experiment of HB pencil lead.

From the table above, it shows there is a significant dropped in the amount of voltage after the it passes through the circuit, when comparing to the reading on the voltmeter after passing through the pencil, the amount of voltage that is passing through originally has dropped. Also this also shows that as we increase the voltage on the power supply, the current will also increase. The range that seems to be most suitable for us to use in our experiment is from 2-6, since the more graphite in the pencil, the higher the current and voltage will be, so if the range is too high the graphite will get too hot, and temperature can alter the resistance of the material. The hotter the pencils lead the resistance increases because the free electrons and the positive ions vibrate more due to an increase in kinetic energy (the heat energy is converted into kinetic energy) so that current is reduced.

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Prediction:

In pencil lead, as the hardness of the lead increases the higher the resistance. This is because the harder the pencil lead is, the greater the proportion of clay is in the lead, this means that it will need a large potential difference (voltage) across it, in order to get a current to flow through it.

Hypothesis:

Pencil lead is made from a combination of finely ground graphite and clay, mixed with water and pressed together it is then heated into thin rods at high temperatures. Graphite is largely made up of carbon, which is ...

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