Question

a sound intensity of 70 dB is observed a distance of d from the source of sound. what sound intensity would be observed at a distance 2d from the source

Answer 1

Correct option is

B

16dB

Sound level at A is ⊥o⊥B

If the intensity of sound at A 4 cm away from the source is I

A

then.

⊥o=10log

I

o

I

A

Where I

o

=10

−12

w m

−2

⇒⊥=log

10

−12

I

A

⇒

10

−12

I

A

=10

⇒I

A

=10

−11

wm

−2

If the source (s) is emmitting the sound energy of power P

I

A

=

4×(4)

2

P

⇒P=10

−11

×64π w

⇒ Intensity of sound (I

B

) ar point B,2 m

I

B

=

4π(2)

2

P

I

B

=

16π

64π×10

−11

10 m

−2

⇒I

B

=4×10

−11

wm

−2

⇒ Sound level at 2m=10log(

I

I

B )

=10log(10 −12

4×10 −11)

=10log40

=16.02

Hence Sound level at 2m from sourceis 16 dB