Physics Homework Help?

Question

At a rock concert, a dB meter registered 126 dB when placed 2.1 m in front of a loudspeaker on the stage. The intensity of the reference level required to determine the sound level is 1.0×10−12W/m2.

Part A

What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?

 

Part B

How far away would the sound level be 82 dB?

 

Answer 1

(A)

Step 1:

The intensity of the sound in decibels is .

The reference level intensity of the sound is .

The loud speaker is placed at a distance of .

The sound is spreading in uniform spherical.

The intensity of sound is , where is output power and is area.

Find the intensity of sound.

The intensity of sound in decibels is , where is intensity of sound and is the reference level intensity of the sound.

.

Step 2:

The area of the uniform spherical is .

.

Substitute and in .

.

The output power is .

Solution:

The output power is .

Answer 2

(B)

Step 1:

The intensity of the sound in decibels is .

From part (A): The output power is .

Find the intensity of the sound.

The intensity of sound in decibels is , where is intensity of sound and is the reference level intensity of the sound.

.

Step 2:

The sound is spreading in uniform spherical.

Find the distance between loud speaker and decibel register.

The intensity of sound is , where is output power and is area.

The area of the uniform spherical is .

.

The distance between loud speaker and decibel register is .

Solution:

The distance between loud speaker and decibel register is .