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GATE 2016 CE (CE2) – Question 61

Air Pollution and Municipal Solid Wastes · Air pollution: pollutants, sources, impacts, control and air quality index · 2 marks · Numerical answer

A noise meter located at a distance of 30 m from a point source recorded 74 dB. The reading at a distance of 60 m from the point source would be _________

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Correct answer: 67 to 69

Explanation

For ideal free-field spherical spreading, intensity varies inversely with distance squared. Sound-level change is−20log10(r2/r1)=−20log10(60/30)=−6.0206dB. New level is74−6.0206=**67.98dB**. This assumes no reflections or additional attenuation.