Question

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

• A. $1 \,ms^{-1}$
• B. $2 \,ms^{-1}$
• C. $3 \,ms^{-1}$
• D. $4 \,ms^{-1}$

Answer 1

Answer: (B)

Here, $\lambda_A = 100\, mm = 0.10 \,m$
$\lambda_B = 0.25 \,m$, $v_A = 80 \,cm \,s^{-1} = 0.80\, ms^{-1}$
As the frequency of the wave remains same in the two media
$\therefore \upsilon = \frac{v_{A}}{\lambda_{A}} = \frac{v_{B}}{\lambda_{B}}$
$\therefore v_{B} = \frac{\lambda _{B}}{\lambda _{A}}\times v_{A} = \frac{0.25}{0.10} \times0.80$
$\Rightarrow v_{B} = 2\,ms^{-1}$