# 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 ′

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

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

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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