Part (a) though a popular question but appeared not to be properly taught in schools because it was poorly attempted by most candidates.
Part (b) was fairly well attempted.
In part (c), the drawing of a projector/projection lantern proved difficult to many candidates. Performance was poor in this part. Part (d) was well fairly attempted.
The expected answers were as follows:
(a) Overtones are integral multiples of fundamental frequency emitted by a musical
instrument.
Valid additional information e.g. the first overtone is the second harmonic.
(b) f = 20Hz λ = 1.2
V = f λ
= 20 x 1.2
= 24 ms-1
But V = x/t
24 = 96/t
t = 96/24 = 4 seconds
(c)(i) Diagram
Converging lens
object
screen
rays
½ will be deducted if:
- u > v,
- no arrow shown
Note: if a projector lantern is not drawn in full and if candidates show lens,
object, screen and rays, score accordingly.
(ii) Instrument is projector or projection lantern
(d) (i) M = Hi
Ho
= 0.8 = 40
0.02
U = V = 4 = 0.1m
40 = 40
(ii) 1 + 1 = 1
U V f
1 + 1 = 1
0.1 4 f
f = 0.0975m
