# NCERT Class 11 Physics Solutions: Chapter 13 – Kinetic Theory-Part 4

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**Question 13.9:**

At what temperature is the root mean square speed of an atom in an argon gas cylinder equal to the rms speed of a helium gas atom at ? (atomic mass of .

**Answer:**

Temperature of the helium atom,

Atomic mass of argon,

Atomic mass of helium,

Let, be the rms speed of argon.

Let be the rms speed of helium.

The rms speed of argon is given by:

Where,

is the universal gas constant

is temperature of argon gas

The rms speed of helium is given by:

It is given that:

Therefore, the temperature of the argon atom is