GATE 2017 CE (CE1) – Question 62

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

Four independent sound sources have levels 60, 69, 70 and 79 dB. Find the equivalent combined sound power level in dB.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 79 to 81

Explanation

Decibel levels must be converted to linear powers before addition: $L=10\log_{10}(10^6+10^{6.9}+10^7+10^{7.9})$. Factoring out $10^8$, the sum is $10^8(0.01+0.0794328+0.1+0.794328)=0.983761\times10^8$. Thus $L=79.93$ dB, approximately 80 dB. Adding the four dB values directly would be invalid.

More Air pollution: pollutants, sources, impacts, control and air quality index questions

GATE 2026 CE (CE2) Q27 – Column I presents common air pollutants, and column II presents treatment technologies…
GATE 2026 CE (CE2) Q65 – In an industry, a cyclone collector with 80 % efficiency is installed for air…
GATE 2025 CE (CE1) Q22 – A hydrocarbon (C nH m) is burnt in air (O 2 + 3.78N 2). The stoichiometric fuel to air…
GATE 2025 CE (CE2) Q63 – A settling chamber is used for the removal of discrete particulate matter from air with…
GATE 2024 CE (CE1) Q31 – The primary air pollutant(s) is/are
GATE 2024 CE (CE1) Q43 – For assessing the compliance with the emissions standards of incineration plants, a…

All Air pollution: pollutants, sources, impacts, control and air quality index questions →