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GATE 2020 AG – Question 27

Farm Power · Tractors and Power Tillers · 1 mark · Numerical answer

A tractor operator experiences sound pressure level 80 dB. Reference pressure is 2×10⁻⁵ N/m². Find RMS sound pressure in N/m² (two decimals).

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Correct answer: 0.19 to 0.21

Explanation

Sound-pressure level is $L_p=20\log_{10}(p/p_0)$. Thus p=p₀10^(80/20)=2×10⁻⁵×10⁴=0.20 N/m². The factor is 20 for pressure amplitude, rather than 10 used for intensity ratios.

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