(a)(i) What is an echo? (ii) State two useful applications of echoes.
(iii) Why are the walls, floors and ceilings of a recording studio heavily padded?
(b)(i) Explain timbre and overtones.
(ii) What is resonance?
(c) As a ship approaches a cliff, its siren is sounded and the echo is heard in the ship after 12 seconds. 2.1 minutes later the siren was sounded again and the echo was heard 8 seconds later. If the speed of sound in air is 340 ms\(^{-1}\), calculate the velocity at which the ship was approaching the cliff.
Explanation
(a)(i) An echo is a reflected sound.
(ii) Echoes can be used to:
- Determine the speed of sound in air.
- Determine the depth of a sea bed.
- Locate the positions of shoals of fish.
- Echo sounding is used in mineral prospecting.
(iii) Padding absorbs sound and minimizes reflections at the walls, floors or ceilings. This helps to minimize the effects of echoes.
(b)(i) Timbre is the characteristic quality of a sound produced by a particular voice or instrument. Timbre of the note is pure and it comes out unaccompanied by undesired notes. Overtones are sound notes which accompany the fundamental notes.
(ii) Resonance is said to occur whenever a particular body or system is set in oscillation at its own natural frequency as a result of impulses received from some other system which is vibrating with the same frequency.
(c) Let S\(_1\) = distance i between the ship and the cliff in the first instance
\(\frac{2S}{12}\) = 340; S\(_1\) = 2040m
In the second instance \(\frac{2S_2}{8}\) = 340
S\(_2\) = 1360m
Distance travelled by ship in 2.1 minute S\(_1\) - S\(_2\)
= 2040 - 1360 = 680m
Ship velocity V = \(\frac{680 }{2.1 \times 60}\) = 5.4ms\(^{-1}\)