Typical fluorescent lamp: 120 cm in length and 3.6 cm in diameter, Ar pressure of 3 Torr.
The electric field between the tube cathode and the anode continuously transfers energy to the electrons. The electrons redistribute the energy among themselves, quickly reaching the temperature on the order of 11,000 K. Similarly, neutral Ar atoms also quickly equilibrated thermally among themselves. However, because of a very large mass mismatch, collisions between electrons and Ar atoms are extremely inefficient in transferring the electrons' energy to Ar atoms. Hence, the argon temperature in a is much lower than the electrons' temperature.
What is the total frequency of electron-Ar collisions in the tube having volume of 4.9e-3 m^3 and concentration of free electrons = 5.0e17 m^-3, the mean collision time of an electron with Ar atoms is 7.9e-10 s?
I did [(4.9e-3)(5.0e17)]/(7.9e-10) = 3.1e24 s^-1 but the answer is 7.9e27.