The GATE Grind

GATE 2021 ES – Question 20

Air and Noise Pollution · Noise Pollution · 1 mark · Multiple choice

For RMS sound pressure p and reference hearing-threshold pressure p₀,which formula gives sound pressure level in dB?

  1. $20\log_{10}(p/p_0)$
  2. $20\log_{10}(p_0/p)$
  3. $20-\log_{10}(p/p_0)$
  4. $20+\log_{10}(p/p_0)$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) $20\log_{10}(p/p_0)$

Explanation

Sound intensity is proportional to pressure squared in a common acoustic medium. Therefore $L_p=10\log_{10}(p^2/p_0^2)=20\log_{10}(p/p_0)$,**A**. Reversing the ratio would give a negative level for pressure above reference.

More Noise Pollution questions

All Noise Pollution questions →