Question

A sound wave has a frequency of 4 kHz and wavelength 30 cm. How long will it take to travel 2.4 km ?
1. 2.0 s
2. 0.6 s
3. 1.0 s
4. 8.0 s

Answer 1

Correct Answer - Option 1 : 2.0 s

Concept:

• The sound waves propagate through the air in different frequencies, among this human ears can only sense the sound of bandwidth 20 Hz-20 kHz.
• Sound waves with a frequency greater than audible waves are known as Ultrasonic waves.
• The wavelength of this wave can be defined as displacement made when a wave complete its one oscillation
• And the relation between wavelength (λ), frequency (n) and velocity (v) can be given as

v = n × λ

\(T=\frac{d}{v}\)

Calculation:

Given:

Frequency (n) = 4 kHz, Wavelength, λ = 30 cm = 0.3 m, Distance, d = 2.4 × 10³ m

The velocity of sound in air v = n × λ = 4 × 10³ × 0.3 = 1.2 × 10³

\(T=\frac{d}{v}=\frac{2.4 \times 10^3}{1.2 \times 10^3}=2\) sec