Environmental Science: Numerical Questions – Noise Change Wrt Distance

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Type I – Point Source

1. A point source of noise produces a sound of 60 dB at a distance of 10 m from it. If the sound is measured at a distance of 40 m, what will be its value ?

  1. 48 dB

  2. 54 dB

  3. 57 dB

  4. 44 dB’

Answer: (A) 48 dB

Explanation: - 20 Log

Where,

- Sound at point 2

- 20 Log

= 60 - 20 Log 4

= 60 – 20*0.60

= 60 – 12

=48 dB

2. A point source of sound produces a noise of 70 dB at a distance of 20 m from it. What will be the noise level at 80 m from it ?

  1. 35 dB

  2. 64 dB

  3. 58 dB

  4. 52 dB

Answer: (C) 58 dB

Explanation: - 20 Log

Where,

- Sound at point

- 20 Log

= 70 - 20 Log 4

= 70 – 20*0.60

= 70 – 12

=58 dB

Type II – Line Source

3. A road carrying heavy traffic has an average noise level of 90 dB when measured at a distance of 10 metres. What would be the noise level at 20 metres distance ?

  1. 87 dB

  2. 84 dB

  3. 60 dB

  4. 45 dB

Answer: (A) 87 dB

Explanation: - 10 Log

Where,

- Sound at point 2

- 10 Log

= 90 - 10 Log 2

= 90 – 10*0.3

= 90– 3

=87 dB

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