Wave and Acoustics | Physics JEE previous year questions with Solutions

Q 1 :
The speed of sound in oxygen at S.T.P. will be approximately:

(Given, $R = 8.3$ $J K^{- 1}, γ = 1.4$ ) [2024]

310 m/s
333 m/s
341 m/s
325 m/s

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(1)

$v = \sqrt{\frac{γ R T}{M}} = \sqrt{\frac{1.4 \times 8.3 \times 273}{32 \times 10^{- 3}}}$

$= 314.8541 ≃ 315 m / s$

Q 2 :
A point source is emitting sound waves of intensity $16 \times 10^{- 8} W m^{- 2}$ at the origin. The difference in intensity (magnitude only) at two points located at distances of 2 m and 4 m from the origin respectively will be ____ $\times 10^{- 8}$ $W m^{- 2} .$ [2024]

0%

(3)

We know for point source, $I \propto \frac{1}{r^{2}} = \frac{K}{4 π r^{2}}$

$r_{1} = 2 m, r_{2} = 4 m = 2 r_{1}$

$I_{0} = 16 \times 10^{- 8} {W/m}^{2}$

at 2m, $I_{1} = \frac{I_{0}}{{(2)}^{2}} = \frac{16 \times 10^{- 8}}{4}$

$I_{1} = 4 \times 10^{- 8}$

At 4m, $I_{2} = \frac{I_{0}}{4^{2}} = \frac{16 \times 10^{- 8}}{16} = 10^{- 8}$

$| I_{2} - I_{1} |$ $= 3 \times 10^{- 8} {W/m}^{2}, x = 3$

Q 3 :
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A) : A sound wave has higher speed in solids than gases.

Reason (R) : Gases have higher value of Bulk modulus than solids.

In the light of the above statements, choose the correct answer from the options given below [2025]

Both A and R true and R is the correct explanation of A.
A is false but R is true.
Both A and R true but R is Not the correct explanation of A.
A is true but R is false.

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(4)

Speed of sound in a medium depends on inertial and elastic properties as $v = \sqrt{\frac{B}{P}}$ for gases and $v = \sqrt{\frac{Y}{P}}$ for solids. Since the elastic property of solid happens to be many folds greater han that of gases, the speed of sound in solids is higher than in gases.

Also, bulk modulus of gases varies between 0 and $\infty (B = - v \frac{d P}{d v})$ hence reason is false.

Q 4 :
Consider the sound wave travelling in ideal gases of He, ${CH}_{4}$ and ${CO}_{2}$ . All the gases have the same ratio $\frac{P}{ρ}$ , where P is the pressure and $ρ$ is the density. The ratio of the speed of sound through the gases $V_{He} : V_{{CH}_{4}} : V_{{CO}_{2}}$ is given by [2025]

$\sqrt{\frac{7}{5}} : \sqrt{\frac{5}{3}} : \sqrt{\frac{4}{3}}$
$\sqrt{\frac{5}{3}} : \sqrt{\frac{4}{3}} : \sqrt{\frac{7}{5}}$
$\sqrt{\frac{5}{3}} : \sqrt{\frac{4}{3}} : \sqrt{\frac{4}{3}}$
$\sqrt{\frac{4}{3}} : \sqrt{\frac{5}{3}} : \sqrt{\frac{7}{5}}$

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(3)

$V_{sound} = \sqrt{\frac{γ P}{ρ}}$

$γ = 1 + \frac{2}{f}$

$γ_{He} = 1 + \frac{2}{3} = \frac{5}{3}$

$γ_{{CH}_{4}} = γ_{{CO}_{2}} = 1.33 = \frac{4}{3}$

$V_{He} : V_{{CH}_{4}} : V_{{CO}_{2}} = \sqrt{\frac{5}{3}} : \sqrt{\frac{4}{3}} : \sqrt{\frac{4}{3}}$

Topic Question Set

Q 1 :
The speed of sound in oxygen at S.T.P. will be approximately:

(Given, $R = 8.3$ $J K^{- 1}, γ = 1.4$ ) [2024]

Q 2 :
A point source is emitting sound waves of intensity $16 \times 10^{- 8} W m^{- 2}$ at the origin. The difference in intensity (magnitude only) at two points located at distances of 2 m and 4 m from the origin respectively will be ____ $\times 10^{- 8}$ $W m^{- 2} .$ [2024]

0%

Q 4 :
Consider the sound wave travelling in ideal gases of He, ${CH}_{4}$ and ${CO}_{2}$ . All the gases have the same ratio $\frac{P}{ρ}$ , where P is the pressure and $ρ$ is the density. The ratio of the speed of sound through the gases $V_{He} : V_{{CH}_{4}} : V_{{CO}_{2}}$ is given by [2025]

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Topic Question Set

Q 1 : The speed of sound in oxygen at S.T.P. will be approximately: (Given, R=8.3 JK-1,γ=1.4) [2024]

Q 2 : A point source is emitting sound waves of intensity 16×10-8Wm-2 at the origin. The difference in intensity (magnitude only) at two points located at distances of 2 m and 4 m from the origin respectively will be ____ ×10-8Wm-2. [2024]

0%

Q 4 : Consider the sound wave travelling in ideal gases of He, CH4 and CO2. All the gases have the same ratio Pρ, where P is the pressure and ρ is the density. The ratio of the speed of sound through the gases VHe : VCH4 : VCO2 is given by [2025]

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Q 1 :
The speed of sound in oxygen at S.T.P. will be approximately:

(Given, $R = 8.3$ $J K^{- 1}, γ = 1.4$ ) [2024]

Q 2 :
A point source is emitting sound waves of intensity $16 \times 10^{- 8} W m^{- 2}$ at the origin. The difference in intensity (magnitude only) at two points located at distances of 2 m and 4 m from the origin respectively will be ____ $\times 10^{- 8}$ $W m^{- 2} .$ [2024]

Q 4 :
Consider the sound wave travelling in ideal gases of He, ${CH}_{4}$ and ${CO}_{2}$ . All the gases have the same ratio $\frac{P}{ρ}$ , where P is the pressure and $ρ$ is the density. The ratio of the speed of sound through the gases $V_{He} : V_{{CH}_{4}} : V_{{CO}_{2}}$ is given by [2025]