The objective of this unit is to bridge theoretical concepts of Statistical Mechanics and Plasma Physics with experimental observations. You will focus on measuring fundamental constants and understanding the behavior of ionized gases.
The Boltzmann constant (k) can be estimated using the V-I characteristics of a P-N junction diode.
By plotting ln(I) vs. V in the forward bias region, the slope of the resulting straight line allows for the calculation of k.
Stefan's Law states that the total power (P) radiated by a blackbody is proportional to the fourth power of its absolute temperature (T).
In the lab, this is often verified using an electric bulb (incandescent lamp). By measuring the resistance of the filament at different voltages, the temperature can be determined, and the relation P \propto T4 can be checked.
This is typically performed using the Photoelectric Effect. By using filters of different colors (wavelengths) and measuring the Stopping Potential (V0), Planck's constant (h) is determined from the slope of the V0 vs. frequency (f) graph.
A Langmuir Probe is a small electrode inserted into a plasma. By varying the potential applied to the probe and measuring the current collected, one can determine the local properties of the plasma.
From the Langmuir probe data, key Plasma Parameters can be calculated:
A Glow Discharge is a plasma formed by the passage of electric current through a low-pressure gas. In this experiment, you observe the distinct luminous regions:
Key Observation: As pressure decreases, the "dark spaces" expand, and the "positive column" may exhibit striations (alternating bright and dark bands).
Tip: When plotting the Langmuir probe data, use a semi-log plot for the electron current. The linear part of this plot is the most reliable way to find the Electron Temperature (Te).