A pipe with 30 cm length is open at both ends. Which harmonic mode of the pipe resonates with the 1.65 kHz source? (Velocity of sound in air $=330 \mathrm{~ms}^{-1}$ )

If the frequency of a wave is increased by $25 \%$, then the change in its wavelength is (medium not changed)

The speed of a wave on a string is $150 \mathrm{~ms}^{-1}$ when the tension is 120 N . The percentage increase in the tension in order to raise the wave speed by $20 \%$ is

Two stretched strings $A$ and $B$ when vibrated together produce 4 beats per second. If the tension applied to the string $A$ increased. The number of beats produced per second is increased to 7. If the frequency of string $B$ is 480 Hz initially, the frequency of string $A$ is