The sketches I to IV in figure below show sound waves, all formed in the same time interval.

Which diagram shows

(i) a note from a musical instrument,

(ii) a soft (or feeble) note,

(iii) a bass (or low frequency) note.

Figure below shows the wave patterns of three sounds A, B and C. Name the characteristic of sound which is same between (i) A and B, (ii) B and C, and (iii) C and A.

Why is the loudness of the sound heard by a plucked wire increased when it is mounted on a sound board?

Define the term intensity of a sound wave. State the unit in which it is measured.