Question

If the wavelength of a wave is decreased by $20\text{\%}$ then its frequency will become :

• A. $20\text{\%}less$
• B. $25\text{\%}more$
• C. $20\text{\%}more$
• D. $25\text{\%}less$

Answer 1

The correct option is B $25\text{\%}more$

Velocity of sound in the air does not change with frequency it means that the product of wavelength and frequency remains constant for different sounds.

$v=f_1\times {\lambda }_1=f_2\times {\lambda }_2$

if, ${\lambda }_2=0.8{\lambda }_1$,

$f_2=f_1\frac{{\lambda }_1}{{\lambda }_2}=f_1\left(1/0.8\right)=1.25{\lambda }_1$

option "B" is correct.