The intensity level $1 m$ away from a source is $60 d B$ . Threshold intensity of hearing is $10^{- 12} W m^{- 2}$ . If there is no loss of sound power in air then intensity level at $2000 c m$ from the source is :

45 d B

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34 d B

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35 d B

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64 d B

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Solution

The correct option is B $34 d B$
$I \propto \frac{1}{r^{2}}$ and $Δ I = I_{1} - I_{2}$
$10 l o g \frac{I_{2}}{I_{0}} = 10 l o g \frac{I_{1}}{I_{0}} - 10 l o g \frac{I_{1}}{I_{2}}$
and $10 l o g \frac{I_{1}}{I_{2}} = 10 l o g 400 = 26.02 d B$
$∴$ intensity level at 2000 cm away is $60 - 26 = 34 d B$

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The intensity level 1 m away from a source is 60 dB. Threshold intensity of hearing is 10−12Wm−2. If there is no loss of sound power in air then intensity level at 2000 cm from the source is :

The correct option is B 34 dBI∝1r2 and ΔI=I1−I210logI2I0=10logI1I0−10logI1I2and 10logI1I2=10log400=26.02dB∴ intensity level at 2000 cm away is 60−26=34dB

The intensity level $1 m$ away from a source is $60 d B$ . Threshold intensity of hearing is $10^{- 12} W m^{- 2}$ . If there is no loss of sound power in air then intensity level at $2000 c m$ from the source is :