# Find the Typical De Broglie Wavelength Associated with a He Atom in Helium Gas at Room Temperature (27 ºC) and 1 Atm Pressure; and Compare It with the Mean Separation Between Two Atoms Under These Conditions. - Physics

Find the typical de Broglie wavelength associated with a He atom in helium gas at room temperature (27 ºC) and 1 atm pressure; and compare it with the mean separation between two atoms under these conditions.

#### Solution

De Broglie wavelength associated with He atom =0.7268 xx 10^(-10) m

Room temperature, T = 27°C = 27 + 273 = 300 K

Atmospheric pressure, P = 1 atm = 1.01 × 105 Pa

Atomic weight of a He atom = 4

Avogadro’s number, NA = 6.023 × 1023

Boltzmann constant, k = 1.38 × 10−23 J mol−1 K−1

Average energy of a gas at temperature T,is given as:

E = 3/2 kT

De Broglie wavelength is given by the relation:

lambda = h/(sqrt(2mE))

Where,

m = Mass of a He atom

= "Atomic weight"/N_A

= 4/(6.023 xx 10^23)

= 6.64 xx 10^(-24) g = 6.64 xx 10^(-27) kg

:. lambda = h/sqrt(3mkT)

= (6.6 xx 10^(-34))/sqrt(3xx6.64 xx10^(-27)xx 1.38 xx 10^(-23) xx 300)

=0.7268 xx 10^(-10 m

We have the ideal gas formula:

PV = RT

PV = kNT

V/N = "kT"/P

Where,

V = Volume of the gas

N = Number of moles of the gas

Mean separation between two atoms of the gas is given by the relation:

r = (V/N)^(1/3) = ("kT"/P)^(1/3)

= [(1.38 xx 10^(-23) xx 300)/(1.01 xx 10^5)]^(1/3)

= 3.35 xx 10^(-9) m

Hence, the mean separation between the atoms is much greater than the de Broglie wavelength.

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#### APPEARS IN

NCERT Class 12 Physics Textbook
Chapter 11 Dual Nature of Radiation and Matter
Q 35 | Page 411