Sum
Calculate the bulk modulus of air from the following data about a sound wave of wavelength 35 cm travelling in air. The pressure at a point varies between (1.0 × 105 ± 14) Pa and the particles of the air vibrate in simple harmonic motion of amplitude 5.5 × 10−6 m.
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Solution
Given:
Wavelength of sound wave
\[\lambda\]= 35 cm =\[35 \times {10}^{- 2} m\]
Pressure amplitude P0 =\[1 . 0 \times {10}^5 \pm 14 Pa\]
Displacement amplitude of the air particles S0 = 5.5 × 10−6 m
Bulk modulus is given by:
Bulk modulus is given by:
\[B = \frac{P_0 \lambda}{2\pi S_0} = \frac{∆ p}{\left( ∆ V/V \right)}\]
On substituting the respective values in the above equation, we get:
\[B = \left( \frac{14 \times 35 \times {10}^{- 2} m}{2\pi\left( 5 . 5 \right) \times {10}^{- 6} m} \right)\]
\[ \Rightarrow B = 1 . 4 \times {10}^5 N/ m^2\]
Hence, the bulk modulus of air is 1.4\[\times\] 105 N/m2.
Concept: Wave Motion
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