Question

A body sends waves $100mm$ long through medium $A$ and $0.25m$ long in medium $B$. If the velocity of waves in medium $A$ is $80cm{s}^{-1}$. The velocity of waves in medium $B$ is

• A. $1m{s}^{-1}$
• B. $2m{s}^{-1}$
• C. $3m{s}^{-1}$
• D. $4m{s}^{-1}$

Answer 1

Answer: (B)

Here, ${\lambda }_A=100mm=0.10m$
${\lambda }_B=0.25m$, $v_A=80cm{s}^{-1}=0.80m{s}^{-1}$
As the frequency of the wave remains same in the two media
$\therefore \upsilon =\frac{v_A}{{\lambda }_A}=\frac{v_B}{{\lambda }_B}$
$\therefore v_B=\frac{{\lambda }_B}{{\lambda }_A}\times v_A=\frac{0.25}{0.10}\times 0.80$
$\Rightarrow v_B=2m{s}^{-1}$