# EOCQ ans 12

```Answers to end-of-chapter questions
Chapter 12
1 a source
7 a trace A
The amplitude of trace A is the greatest.
b vibrations
b trace C
The frequency of trace C is the greatest
(because more waves are contained in
the same time interval).
c echo
d frequency; second
e hertz
8 You need a source of sound,
f gases; vacuum
and two detectors in line with the sound.
You need to measure the distance between
the two detectors,
and the time interval between the sound
reaching them.
distance
Then use speed =
time
to calculate the speed of sound.
2 a greater frequency
b greater amplitude
3 a
B A
b
D
9 a solid
C
4 a shaded from 20 Hz to 20 kHz
b region beyond 20 kHz
5
rarefaction
where particles of the medium are
compression
where particles of the medium are
squashed together
6 a the air inside the instrument
[1]
b the strings of the instrument
[1]
c The vibrations of the instrument cause
the air near the instrument to vibrate.
Compressions and rarefactions
are formed,
and these propagate through the air
to the listener’s ear.
© Cambridge University Press 2014 IGCSE Physics
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b (for example) Place ear against table,
tap table at a distance
and hear the sound through the wood.
[1]
[1]
c distance travelled = 2 times length
of rod
= 800 m
[1]
distance
time
[1]
800 m
0.16 s
[1]
= 5000 m/s
[1]
speed =
=
10 a i
reflection or wave bounces back
from large object/sea bed
[1]
[1]
[1]
ii distance = speed × time
= 1500 × 0.80
= 1200 (m)
[1]
[1]
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iii 1200/2 = 600 (m)
[1]
b graph should show
uniformly sloping line
[1]
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Answers to end-of-chapter questions: Chapter 12
1
11 a any large surface, e.g. wall/cliff/mountain
b i when hears bang/sees flash
ii when hears echo
c i reading = 2.25 s
speed = distance
time
[1]
[1]
[1]
[1]
[1]
= 720
2.25
[1]
= 320 (m/s)
[1]
ii one from
inaccurate distance from firework
reaction time
wind
© Cambridge University Press 2014 IGCSE Physics
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Answers to end-of-chapter questions: Chapter 12
2
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