Question

Sound waves travel at $$350\,m/s$$   through a warm air and at $$3500\,m/s$$   through brass. The wavelength of a $$700\,Hz$$   acoustic wave as it enters brass from warm air

A. increases by a factor 20
B. increases by a factor 10  
C. decreases by a factor 20
D. decreases by a factor 10
Answer :   increases by a factor 10
Solution :
Velocity of a wave is given by
\[v = n\lambda \,\,\left[ {\begin{array}{*{20}{c}} {n = {\text{frequency of wave}}} \\ {\lambda = {\text{wavelength of wave}}} \end{array}} \right]\]
So, for two different cases,
$$\eqalign{ & {v_1} = {n_1}{\lambda _1} \cr & {v_2} = {n_2}{\lambda _2} \cr & {\lambda _2} = {\lambda _1}\frac{{{v_2}}}{{{v_1}}} = {\lambda _1} \times \frac{{3500}}{{350}} = {\lambda _1} \times 10\,\left[ {\because {n_1} = {n_2}} \right] \cr & {\lambda _2} = 10\,{\lambda _1} \cr} $$

Releted MCQ Question on
Oscillation and Mechanical Waves >> Waves

Releted Question 1

A cylindrical tube open at both ends, has a fundamental frequency $$'f'$$ in air. The tube is dipped vertically in air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column in now

A. $$\frac{f}{2}$$
B. $$\frac{3\,f}{4}$$
C. $$f$$
D. $$2\,f$$
Releted Question 2

A wave represented by the equation $$y = a\cos \left( {k\,x - \omega t} \right)$$    is superposed with another wave to form a stationary wave such that point $$x = 0$$  is a node. The equation for the other wave is

A. $$a\sin \left( {k\,x + \omega t} \right)$$
B. $$ - a\cos \left( {k\,x - \omega t} \right)$$
C. $$ - a\cos \left( {k\,x + \omega t} \right)$$
D. $$ - a\sin \left( {k\,x - \omega t} \right)$$
Releted Question 3

An object of specific gravity $$\rho $$ is hung from a thin steel wire. The fundamental frequency for transverse standing waves in the wire is $$300\,Hz.$$  The object is immersed in water so that one half of its volume is submerged. The new fundamental frequency in $$Hz$$  is

A. $$300{\left( {\frac{{2\,\rho - 1}}{{2\,\rho }}} \right)^{\frac{1}{2}}}$$
B. $$300{\left( {\frac{{2\,\rho }}{{2\,\rho - 1}}} \right)^{\frac{1}{2}}}$$
C. $$300\left( {\frac{{2\,\rho }}{{2\,\rho - 1}}} \right)$$
D. $$300\left( {\frac{{2\,\rho - 1}}{{2\,\rho }}} \right)$$
Releted Question 4

A wave disturbance in a medium is described by $$y\left( {x,t} \right) = 0.02\cos \left( {50\,\pi t + \frac{\pi }{2}} \right)\cos \left( {10\,\pi x} \right)$$        where $$x$$ and $$y$$ are in metre and $$t$$ is in second

A. A node occurs at $$x = 0.15\,m$$
B. An antinode occurs at $$x = 0.3\,m$$
C. The speed wave is $$5\,m{s^{ - 1}}$$
D. The wave length is $$0.3\,m$$

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Waves


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