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Question: According to Newton’s formula, the speed of sound in air at STP is (Take the mass of 1 mole of air ...

According to Newton’s formula, the speed of sound in air at STP is

(Take the mass of 1 mole of air is 29 × 10–3 kg)

A

250 m s–1

B

260 m s–1

C

270 m s–1

D

280 m s–1

Answer

280 m s–1

Explanation

Solution

1 Mole of any gas occupies 22.422.4litres at STP.

Therefore, density of air at STP is

ρ=MassofonemoleofairVolumeofonemoleofairatSTP\rho = \frac{Massofonemoleofair}{VolumeofonemoleofairatSTP}

=29×10−3kg22.4×10−3m3=1.29kgm−3= \frac{29 \times 10^{- 3}kg}{22.4 \times 10^{- 3}m^{3}} = 1.29kgm^{- 3}

At STP, P = 1 atm = 1.01×105Nm−21.01 \times 10^{5}Nm^{- 2}

According to Newton’s formula, the speed of sound in air at STP is

v=(Pρ)=1.01×10−3Nm−21.29×kgm−3=280ms−1v = \sqrt{\left( \frac{P}{\rho} \right)} = \sqrt{\frac{1.01 \times 10^{- 3}Nm^{- 2}}{1.29 \times kgm^{- 3}}} = 280ms^{- 1}