The fundamental frequency of a sonometer wire is 50 Hz for some length and tension. If the length is increased by $25 \%$ by keeping tension same then frequency change of second harmonic is

When source of sound and observer both are moving towards each other, the observer will hear

The lengths of the two organ pipes open at both ends are ' L ' and $\left(\mathrm{L}+\mathrm{L}_1\right)$. If they are sounded together, the beat frequency will be ( $\mathrm{v}=$ velocity of sound in air)

A person standing between two parallel cliffs fires a gun and hears two echoes, first echo after 1 second and the second echo after 3 second. The distance between the two cliffs is (Velocity of sound $=340 \mathrm{~m} / \mathrm{s}$ )