## Question

### Solution

Correct option is

32 Hz

Let the frequency of the first tuning fork be V. The frequency of the second will be (V + 4) and of the third will be (V + 8) and so on. Now V + 8 = V + (3 – 1) × 4. Therefore, the frequency of the 9th tuning fork = V + (9 – 1) × 4 = V + 32. It is given that V + 32 = 2V. Hence V = 32 Hz.

#### SIMILAR QUESTIONS

Q1

(a) The power of sound from the speaker of a radio is 20 mW. By turning the knob of volume control the power of sound is increased to 400 mW. What is the power increase in dB as compared to original power?

(b) How much more intense is an 80 dB sound than a 20 dB whisper?

Q2

A window whose area is 2 m2 opens on a street where the street noise result in an intensity level at the window of 60 dB. How much ‘acoustic power’ enters the window via sound waves. Now if an acoustic absorber is fitted at the window, how much energy from street will it collect in five hours?

Q3

A dog while barking delivers about 1 mW of power. If this power is uniformly distributed over a hemispherical area, what is the sound level at a distance of 5 m? What would the sound level be if instead of 1 dog, 5 dogs start barking at the same time each delivering 1 mW of power?

Q4

An observer is at a distance of one metre from a point light source whose power output is 1 kW. Calculate the magnitude of electric and magnetic fields assuming that the source is monochromatic, it radiates uniformly in all directions and that at the point of observation it behaves like a travelling plane wave. Given that H/m and Q5

A wave pulse starts propagating in +x-direction along a non-uniform wire of length 10 m with mass per unit length given m = m0 + αx and under a tension of 100 N. Find the time taken by the pulse to travel from the lighter end (x = 0) to the heavier end. (m0 = 10–2 kg/m and α = 9 × 10–3 kg/m2)

Q6

Decibel is:

Q7

The variation of the speed of sound with temperature is greatest in:

Q8

The speed of sound in hydrogen at STP is v. The speed of sound in a mixture containing 3 parts of hydrogen and 2 parts of oxygen at STP will be

Q9

The speed of sound in hydrogen at STP is v. What is the speed of sound in helium at STP?

Q10

A sonometer wire of length 120 cm is divided into three segments of lengths in the ratio of 1: 2: 3. What is the ratio of their fundamental frequencies?