What is a trough?

How does the sound produced by a musical instrument reach your ears? Astronauts need radio transmitters to talk to each other on the moon. Why?

$A$ note is a sound:

State whether the following statement is true or false:
Light waves require no medium for their propagation.

$(a)$ List in tabular form the distinguishing features between longitudinal waves and transverse waves. Give an example of each.
$(b)$ State and define the characteristics associated with sound waves.

State whether the following statement is true or false:
Sound travels faster at a higher temperature than at a lower temperature.