When we change a feeble sound to a loud sound,we increase its:

$(a)$ $A$ particular transmitter of Aakashvani broadcasts at $420.5\, m$ wavelength. Given the speed of radio waves $3 \times 10^{8}\, m s^{-1}$. Calculate the frequency at which the radio station broadcasts its programme.
$(b)$ What is the direction of oscillations of the medium particles through which a
$(i)$ transverse wave is propagating?
$(ii)$ longitudinal wave is propagating?

The distance between two consecutive crests in a wave is known as:

Explain why there is usually a time delay between observing a flash and hearing a thunder?

$A$ bomb explodes on the Moon. How long will the sound of the explosion take to reach the Earth?

Explain why echoes cannot be heard in a small room.