Question

A sound wave of wavelength 90 cm in glass is reflected into air. If the speed of sound in glass is 5400 m//s, the wavelength of wave in air (speed of sound in air = 330 m//s) is :

Answer 1

Explanation:

wavelength is proportional to speed, since frequency is constant.

wavelength = 90*330/5400 = 5.5 m

Answer 2

Answer:

A sound wave of wavelength 90 cm in glass is reflected into the air. If the speed of sound in glass is 5400 m//s, the wavelength of the wave in the air (speed of sound in air = 330 m//s) is : $0.055\ m$

Explanation:

• Consider a wave of frequency f and wavelength $\lambda$ then, we have the expression for velocity (v) as,

        $v=f \lambda$      

       that is,

       $f = \frac{v}{\lambda}$      ...(1)

       or

       $\lambda= \frac{v}{f}$      ...(2)

• Since the source of the wave is the same, the frequency of waves produced in water and glass will have the same value.

       

In the question, it is given that,

the wavelength of sound in glass      =   $90\ cm = 0.90m$

the speed of sound in glass               =    $5400\ m/s$

Using equation(1),

frequency of sound,

$f = \frac{5400}{0.90} = 6000 Hz$

Given,

The velocity of sound in air  =    $330\ m/s$

Using equation(2),

wavelength in air                   =    $\frac{330}{6000} = 0.055\ m$