Question

What is the intensity level of a sound with an intensity of 3.5 x 10^-8 W/m²?

	35.4 dB
	49.1 dB
	45.4 dB
	13.4 dB

Two cellos are being played in a duet. At a certain point, one cello plays a note of frequency 196 Hz and the other plays a note of frequency 220 Hz. What is the period of the beat?

	0.4 s
	4 s
	0.25 s
	0.1 s

Answer 1

Part A.

Relation between sound level and Intensity is given by:

SL = 10*log (I/I0)

I = Intensity of sound = 3.5*10^-8 W/m^2

I0 = Human threshold intensity = 10^-12 W/m^2

So,

SL = 10*log (3.5*10^-8/10^-12)

SL = 10*log (3.5*10^4)

SL = 45.4 dB

Part B.

Period of the beat frequency will be:

Beat frequency = f2 - f1 = 220 - 196

Beat frequency = 24 Hz

Now

Period = 1/Beat frequency

Period = 1/24 = 0.04 sec

None of the given options are correct

(I believe 2nd frequency is 200 Hz, then beat frequency = 200 - 196 = 4 Hz, Period = 1/4 = 0.25 sec)

Let me know if you've any query.