Question

The siren on an ambulance is emitting a sound whose frequency is 2450 Hz. The speed of sound is 343 m/s. If the ambulance is stationary and you (the "observer") are sitting in a parked car, what are the wavelength and the frequency of the sound you hear?

Answer 1

Answer:

The wavelength is 0.14 m

Explanation:

Given that,

Frequency = 2450 Hz

Speed of sound = 343 m/s

We need to calculate the wavelength

Using formula of wavelength

$v=  f\lambda$

Where, v = speed of sound

f = frequency

Put the value into the formula

$\lambda=\dfrac{v}{f}$

$\lambda=\dfrac{343}{2450}$

$\lambda=0.14\ m$

Hence,  The wavelength is 0.14 m

Answer 2

Explanation:

It is given that,

Frequency of the siren, f = 2450 Hz

The speed of sound, v = 343 m/s

Here, both ambulance and the observer is stationary. The observed frequency is calculated using Doppler's effect as :

$f'=\dfrac{v+v_o}{v-v_s}\times f$

$v_o$ is the velocity of observer

$v_s$ is the velocity of source

v is the speed of sound wave

Here, $v_o=v_s=0$

So, f' = f

f' = 2450 Hz

Wavelength, $\lambda'=\dfrac{v}{f'}$

$\lambda'=\dfrac{343\ m/s}{2450\ Hz}$

$\lambda'=0.14\ m$

So, the frequency and wavelength of the observed sound is 2450 Hz and 0.14 meters. Hence, this is the required solution.