Question

Sound waves travel at $350 \,ms^{-1}$ through a warm air and at $3500\, ms^{-1}$ through brass. The wavelength of a $700\, Hz$ acoustic wave as it enters brass from warm air

• A. decrease by a factor $10$
• B. increase by a factor $20$
• C. increase by a factor $10$
• D. decrease by a factor $20$

Answer 1

Answer: (C)

Velocity of sound $v=n \lambda$
$\frac{v_{1}}{v_{2}} =\frac{n_{1} \lambda_{1}}{n_{2} \lambda_{2}} $ (but $n_{1}=n_{2}$)
$\lambda_{2} =\lambda_{1} \frac{v_{2}}{v_{1}}=\lambda_{1} \times 10$
$\lambda_{2} =10 \lambda_{1}$