What change,if any,would you expect in the characteristics of musical sound when we increase $(i)$ its frequency and (ii) its amplitude?

Two friends were playing on identical guitars whose strings were adjusted to give notes of the same pitch. Will the quality of the two notes be the same? Give a reason for your answer.

Bats have no eyes,yet they can ascertain the distance,direction,nature,and size of objects. Explain why.

$A$ laboratory uses an ultrasonic scanner to trace a tumour in tissue. The operating frequency of the scanner is $4.2 \times 10^{6} \text{ Hz}$. Calculate the wavelength of sound in the tissue if the speed of the sound is $1700 \text{ m s}^{-1}$.

Answer the following:
$(i)$ Can transverse waves travel in gases?
$(ii)$ Can longitudinal waves travel in solid,liquid as well as gas?
$(iii)$ At any instant,a compression is formed at a point. After how much time $(a)$ a rarefaction $(b)$ a compression will be formed at the same point?

$A$ hospital uses an ultrasonic scanner to locate tumours in a tissue. What is the wavelength of sound in a tissue in which the speed of sound is $1.7 \, km \, s^{-1}$? The operating frequency of the scanner is $4.2 \, MHz$ $(1 \, MHz = 10^{6} \, Hz)$.