Question

A light wave and a sound wave have same frquency f and their wavelengths are respectively ${\lambda }_L$ and ${\lambda }_S$ . then,

• A. ${\lambda }_L={\lambda }_S$
• B. ${\lambda }_L>{\lambda }_S$
• C. ${\lambda }_L<{\lambda }_S$
• D. ${\lambda }_L=2{\lambda }_S$

Answer 1

Answer: (B)

${\lambda }_L>{\lambda }_S$

Frequency of light wave = f
Frequency of sound wave = f
$\therefore$ Wavelength of light waves ${\lambda }_L=c/f$ ...(i)
where, c = velocity of light
and wavelength of sound waves ${\lambda }_s=v/f$
v = velocity of sound
$\therefore \frac{{\lambda }_L}{{\lambda }_S}=\frac{c/f}{v/f}=\frac{c}{v}$
but $c>>>v\Rightarrow \frac{c}{v}>>>1$
$\Rightarrow \frac{{\lambda }_L}{{\lambda }_S}={\lambda }_L>>>{\lambda }_S$