Sound Pressure Definition
Sound pressure is defined as the difference between the instantaneous total pressure and the ambient (or mean) atmospheric pressure at a point in a medium, caused by the passage of a sound wave.
Relating Pressure Components
Sound waves cause fluctuations in the surrounding air pressure. The total pressure at any point includes the steady atmospheric pressure plus these fluctuations.
- Atmospheric Pressure (or Barometric Pressure): This is the average pressure of the atmosphere under normal conditions.
- Total Pressure: This is the instantaneous pressure, including both the atmospheric pressure and the pressure variations due to the sound wave.
- Sound Pressure (or Acoustic Pressure): This is the fluctuating part, representing the change from the average atmospheric pressure.
Calculating Sound Pressure
Mathematically, sound pressure ($p$) can be expressed as:
$ p = P_{total} - P_{atm} $
Where:
- $p$ is the sound pressure.
- $P_{total}$ is the total instantaneous pressure.
- $P_{atm}$ is the ambient atmospheric pressure (also referred to as barometric pressure in this context).
Therefore, sound pressure is specifically the variation above and below the atmospheric pressure.
Evaluating the Options
Based on the definition:
- Option 1 is incorrect because sound pressure is not the total atmospheric pressure itself.
- Option 2 correctly states that sound pressure is the difference between the total atmospheric pressure and the barometric pressure.
- Option 3 is incorrect as sound pressure is not just the barometric pressure.
- Option 4 is incorrect as sound pressure is a difference, not a sum.
The correct option accurately represents sound pressure as the deviation from the ambient atmospheric pressure.
Important Questions from Air and Noise Pollution - Teaching
- Which of the following air pollutants are responsible for photochemical smog ?
(a) Oxides of nitrogen
(b) Ozone
(c) Unburnt hydrocarbons
(d) Sulphur dioxide
Choose the correct code : If [$_env$ < [$_d$ ,where [$_env$ and [$_d$ are environmental & dry adiabatic lapse rates respectively ,which of the following types of plume emitted from a stack of a thermal power plant is observed ?
- The photodissociation of $NO_{2}$ yields which oxygen species ?
- On take - off, an aeroplane generates noise level of 120 dB. If 5 such aeroplanes take - off simultaneously what will be the noise level ?
- Given below are two statements. One labelled as Assertion (A) and the other labelled as Reason (R) :
Assertion (A) : $NO_{X}$ and volatile organic compounds (VOCs) are primary precursors in photochemical smog formation.
Reason (R) : $NO_{X}$ and VOCs form oxidants by thermal reactions.
Choose the correct answer :
