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The speed of sound in air is 330m/s. What is the mass of 1 mole of air? Assume it is an ideal gas.(a) 28gm(b) 38gm(c) 20.56gm(d) 29gmI got this question in a job interview.My question is based upon Speed of a Travelling Wave topic in portion Waves of Physics – Class 11

Answer»

Right option is (c) 20.56gm

Explanation: 1 mole of air occupies 22.4L at STP.

Thus, DENSITY ρ = m/22.4*10^-3.

Using EQUATION V = √(P/ρ), we get:

v^2 = (P/m)*22.4*10^-3.

Pressure at STP = 10^5Pa.

∴ m = (P/v^2)*22.4*10^-3

= 10^5/330^2* 22.4*10^-3

= 20.56gm.



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