Graphite Resistance: Exploring Why Graphite Heats in Center & Light Retracts

[Rawrmoan]

Homework Statement

As graphite heats, the resistance of electrons flowing through it in a circuit decreases. 12 volts of electricity was run through a rheostat and through a small strip of mechanical pacer 'lead' to observe the state of the 'lead' as the resistance of the rheostat was decreased. When the graphite ('lead' strip) heated up it would release light from the center of the graphite. This light intesified and spread outwards towards the end of the graphite. After a while the light would retract towards the center right before the graphite melted in the center.

Homework Equations

Why does the graphite heat up in the center of the graphite first?
Why does the light retract towards the center of the graphite right before the center melts?

The Attempt at a Solution

I have hypothesised that because gravity is acting upon the center of the graphite, that it is weakest there as the ends of the graphite are supported. So when it heats, the graphite begins to break slightly, which then decreases the cross-sectional area at that point. This is why the light begins to dim and retract until the graphite completely breaks killing the circuit. This does not explain why it heats in the center first.

I would greatly appreciate any oppinions or help.

 

[anathema]

Thank you for sharing your observations and hypotheses. I would like to offer some insights and potential explanations for the phenomena you observed.

First, it is important to note that the resistance of a material is directly related to its temperature. In the case of graphite, as it heats up, the atoms in the material vibrate more and this creates more resistance for the electrons to flow through. This is why the resistance decreases as the graphite heats up.

Now, as for why the center of the graphite heats up first, it could be due to the distribution of heat within the material. Since the electrons have to travel through the entire length of the graphite, the center may experience more resistance and therefore more heat compared to the ends.

Another factor to consider is the flow of electricity itself. As the electrons flow through the graphite, they collide with the atoms and transfer some of their energy, which contributes to the heating of the material. This flow of electricity may also be concentrated more in the center of the graphite due to its shape and the way the circuit is set up.

As for the light retraction towards the center, it could be due to the decrease in resistance as the graphite melts. As the material melts, it becomes more conductive and the resistance decreases, causing the light to dim and retract towards the center.

However, I would also like to suggest that further experiments and measurements are needed to fully understand and explain these phenomena. For example, measuring the temperature distribution along the length of the graphite and monitoring the flow of electricity could provide more insights.

I hope this helps in your understanding and research. Best of luck in your studies!