# Audio Engineering MCQ Questions and Answers – Pressure and Intensity of Sound Waves – 1

This set of Audio Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Pressure and Intensity of Sound Waves – 1”.

1. The minimum pressure fluctuation to which our ear can respond is less than one billionth of atmospheric pressure.
a) True
b) False

Explanation: Sound wave consists of very small periodic variations in atmospheric pressure which is responded by our ears in a rather complex manner. Thus, the minimum pressure fluctuation to which our ear can respond is less than one billionth (10-9) of atmospheric pressure.

2. The threshold of audibility does not vary from person to person.
a) True
b) False

Explanation: The minimum pressure fluctuation to which our ear can respond is less than one billionth (10-9) of atmospheric pressure. The threshold of audibility varies from person to person which corresponds to sound pressure amplitude of about 2 × 10-5 N / m2 at a frequency of 1 KHz.

3. How much times greater is the threshold of pain corresponding to pressure amplitude of the atmospheric pressure?
a) 10 million
b) 1 billion
c) 1 trillion
d) 1 million

Explanation: Threshold of pain is defined as minimum intensity at which the pain is felt. The threshold of pain corresponds to a pressure amplitude approximately one million (106) times greater, but still less than 1/1000 of atmospheric pressure.

4. Which scale is often convenient to measure sound pressures on a logarithmic scale?
a) Amplitude
b) Decibel
c) Threshold
d) Temperature

Explanation: Because of the wide range of pressure from 10-9 to 106 N/m2 it is often convenient to measure sound pressures on a logarithmic scale, called the decibel (dB) scale. Despite the fact that the decimal scale is actually a means of comparing two sounds, we can define decibel scale of sound level by comparing sounds with a reference sound having pressure amplitude of p0 = 2 × 10-5 N / m2.

5. Which is the correct expression of sound pressure level?
a) LP = 20 log P/P0
b) LP = 10 log P/P0
c) LP = 30 log P/P0
d) LP = 40 log P/P0

Explanation: Sound pressure level can be defined as LP = 20 log P/P0. Where LP is the pressure level of sound and P is the pressure. Sound pressure levels are measured by a sound level meter called a dB meter.
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6. Which is the correct expression of sound power level?
a) LW = 20 log W/W0
b) LW = 20 log P/W0
c) LW = 10 log W/W0
d) LW = 30 log W/W0

Explanation: The sound power level identifies total sound power emitted by a source in all directions. Thus, sound power level can be defined as LW = 10 log W/W0. Where W is the sound power emitted by the source and the reference power W0 = 10-12 watt/m2.

7. What is the term for audible sound when sound pressure is 20 × 10-6 Pa?
a) Threshold of hearing
b) Threshold of pain
c) Threshold of intensity
d) Threshold of sound

Explanation: When sound pressure is 20 × 10-6 Pa, it gives just the audible sound and it is called threshold of hearing. This much sound pressure pertains to 1 Picowatt/m2 of sound intensity.

8. At what sound pressure is the pain felt?
a) 53 Pa
b) 63 Pa
c) 73 Pa
d) 103 Pa

Explanation: The proportion between sound pressure level (LP) and sound power level (LW) depends on many different factors. The sound pressure at which pain is felt is a 63 Pa, which in terms of intensity is called ‘threshold of pain’ or ‘threshold of feeling’ (its intensity is 10 watt/m2).

9. What is the sound pressure level of a quiet home?
a) 63 × 10-5 Pa or N/m2
b) 20 × 10-6 Pa or N/m2
c) 36 × 10-5 Pa or N/m2
d) 33 × 10-5 Pa or N/m2

Explanation: Sound pressure level (LP) is measured by a sound level meter called a dB meter. Here, quiet home is the type of sound. The sound pressure level of a quiet home is 63 × 10-5 Pa or N/m2 and the intensity is 1 × 10-9.

10. What is the sound pressure level of a normal conversation?
a) 20 × 10-3 Pa or N/m2
b) 33 × 10-5 Pa or N/m2
c) 36 × 10-5 Pa or N/m2
d) 63 × 10-5 Pa or N/m2

Explanation: There are many factors on which the proportion between sound pressure level (LP) and sound power level (LW) depends. Here, normal conversation is the type of sound. The sound pressure level of a normal conversation is 20 × 10-3 Pa or N/m2Pa or N/m2 and the intensity is 1 × 10-6.

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