Environmental Science: Numerical Questions – Noise Addition of Noise

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1. A person is exposed to two sound levels of 80 dB and 100 dB simultaneously. What is the average noise level the person experiences ?

  1. ~ 97 dB

  2. ~ 87 dB

  3. ~ 90 dB

  4. ~ 93 dB

Explanation: 𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^(𝐿_1/10)+10^(𝐿_2/10) )

𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^(80/10)+10^(100/10) )

𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^8+10^10 )

𝐿_𝑒𝑞= 10 𝐿𝑜𝑔 [108(1+10^2 )]

𝐿_𝑒𝑞= 10 [𝐿𝑜𝑔 108” + log 1+ log 102” ]

𝐿_𝑒𝑞= 10 [“8 + 0+2” ]

𝐿_𝑒𝑞= 100 dB

Difference and Added to Higher Sound Value
Difference and Added to Higher Sound Value

Difference (L2-L1)

Added to Higher Sound Value

0

3

1

2.5

2

2.1

3

1.5

4

1.5

5

1

6

1

7

0.8

8

0.6

9

0.5

10

0.4

Difference and Added to Higher Sound Value
Difference and Added to Higher Sound Value

Difference (L2-L1)

Added to Higher Sound Value

0 or 1

3

2 or 3

2

4 to 8

1

9 or more

0

2. On take - off, an aeroplane generates noise level of 120 db. If 5 such aeroplanes take – off simultaneously what will be the noise level ?

  1. ~ 126.98 dB

  2. ~ 124.98 dB

  3. ~ 123.86 dB

  4. ~ 122.98 dB

Answer: (A) ~ 126.98 dB

Explanation: 𝐿_𝑒𝑞= 𝐿_𝑖+10 𝐿𝑜𝑔(𝑛)

𝐿_𝑒𝑞=120+10 𝐿𝑜𝑔(5)

𝐿_𝑒𝑞=120+10∗0.69

𝐿_𝑒𝑞=120+6.9

𝐿_𝑒𝑞=126.9

3. The resultant of two noise levels of 50 dB and 55 dB is:

  1. 58 dB

  2. 55.41 dB

  3. 52.5 dB

  4. 56.19 dB

Answer: Option (D) 56.19 dB

Explanation: 𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^(𝐿_1/10)+10^(𝐿_2/10) )

𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^(50/10)+10^(55/10) )

𝐿_𝑒𝑞= 10 𝐿𝑜𝑔(10^5+10^5.5 )

𝐿_𝑒𝑞=10 Log[10^5 (1+10^0.5)]

𝐿_𝑒𝑞= 10 (𝐿𝑜𝑔 105+log (1+√10)

𝐿_𝑒𝑞= 10 (𝐿𝑜𝑔 105+ log (1+3.16)

𝐿_𝑒𝑞= 10 (5+0.619)

𝐿_𝑒𝑞= 10 ∗5.619=56.19

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