Calculate the pressure in a pure hydrogen gas at T 12000K t

Calculate the pressure in a pure hydrogen gas at T = 12000K that has 20% of its atoms in ionisation state H_{III (}Assume U_I = 2)

Saha Equation problem. Problem #1.11 in \'An Introduction to Stellar Astrophysics\' LeBlanc.

Use the Saha Equation with the following values for the constants: k=1.38×1023 J/K, h=6.63×1034Js, mr = 0.9995me me = 9.11×1031 kg,

i = 13.6eV = 2.18×1018 J,

Since a hydrogen ion is just a proton, there is only one possible energy state so gr+1 = 1.

Neutral hydrogen has gr=gn=2n2

At T=12000K most of the atoms can be found in the ground state.

At T=12000 K, NHII/NH = 50.5

The fraction of ionized atoms is

NHII / Ntotal = NHII / (NH + NHII)

= NHII/ [NH 1 + (NHII/NH)]------------------------(1)

so at at T=12000K 98% of hydrogen atoms are ionized.

and Pe = 20 N/m2