Question:

At \(T(K)\), the rms velocity of an ideal gas is \(x\,\text{m s}^{-1}\). At what temperature (in K), the rms velocity becomes \(3x\,\text{m s}^{-1}\)?

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For an ideal gas: \[ v_{rms} \propto \sqrt{T} \] If speed becomes \(n\) times, temperature becomes \(n^2\) times.
Updated On: Oct 6, 2026
  • \(3T\)
  • \(4T\)
  • \(9T\)
  • \(18T\)
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The Correct Option is C

Solution and Explanation

Concept: The rms speed of an ideal gas is given by: \[ v_{rms} = \sqrt{\frac{3RT}{M}} \] Thus: \[ v_{rms} \propto \sqrt{T} \] This means: \[ \frac{v_2}{v_1} = \sqrt{\frac{T_2}{T_1}} \] Therefore, when rms speed changes, temperature changes as the square of speed ratio.

Step 1: Write the proportional relation. Initially: \[ v_1 = x \] at temperature: \[ T_1 = T \] Finally: \[ v_2 = 3x \] Required temperature: \[ T_2 = ? \] Using: \[ \frac{v_2}{v_1} = \sqrt{\frac{T_2}{T_1}} \]

Step 2: Substitute the values. \[ \frac{3x}{x} = \sqrt{\frac{T_2}{T}} \] \[ 3 = \sqrt{\frac{T_2}{T}} \] Squaring both sides: \[ 9 = \frac{T_2}{T} \] Thus: \[ T_2 = 9T \]

Step 3: Write the final answer. Hence, required temperature is: \[ \boxed{9T} \] Therefore, the correct option is: \[ \boxed{(C)} \]
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