454 © Pearson
7
L
Sound
and the equipment detects the echoes. It works out
the distance to the reflecting object using the time
and the speed of sound in the medium.
7 for cleaning delicate items and in physiotherapy
7Ld-7 Mapping the deep
1 a If the weight continues to be lowered after it
has touched the bottom, too much rope will be let
out and the measurement will be deeper than the
true value.
b If the person lowering the weight thinks it has
touched the bottom before it really has reached
the bottom, then not enough line will have been let
out and the measurement will be less than the true
value.
2 If the ship is blown away, the rope will not
be going vertically downwards, so there will be
more rope let out than there should be and the
measurement will be deeper than the true value.
3 a percentage = 3/300 × 100% = 1%
b percentage = 3/5000 × 100% = 0.06%
4 The time for the echo will be shorter than for the
true depth, and so the measured depth will be less
than the true value.
5 a distance = speed × time = 1500 m/s × 0.4s =
600 m, water depth = 300 m
(or time for half the journey = 0.2 s, depth =
1500m/s × 0.2 s = 300 m)
b The sound will have travelled further in the
measured time, so the real depth will be greater
than the measured depth.
c actual distance travelled = 1550 × 0.4 s = 620
m, actual depth = 310 m
percentage error = 10/300 × 100% = 3.3%
6 Speed of sound – for 300 m depth the
percentage error from waves is much smaller than
that from possible errors in the speed of sound.
7 Some points that could be included in the
answer: measurements at the surface will not
necessarily provide information about the
speed of sound at depth; measurements could
be taken at various depths, but this could take
a long time.
7Ld Working with sound (STEM)
1 a Any sensible suggestions, such as students
talking, bells, doors banging, footsteps, traffic noise
from outside.
b Any sensible mitigation ideas related to the
original suggestions, such as not talking/talking
more quietly, making the bells quieter, walking
instead of running, etc.
2 a Any sensible suggestions such as near roads,
railways or airports, inside or outside factories,
roadworks, in concerts, in houses with music
playing/noisy neighbours.
b Any sensible mitigation idea related to the
original suggestions, such as noise barriers, using
softer/absorbent materials in walls/ceilings, wearing
ear defenders, turning music players down, etc.
3 Metal – Advantages: strong, long lasting/will not
rot. Disadvantage: will reflect sounds back to the
road, so noise may be worse for drivers.
Wood – Advantage: will absorb some of the noise,
so making the road itself quieter than with a metal
barrier. Disadvantage: will not last as long/may rot.
4 a The company will want to record only the
music being played, and not any echoes or
other sounds. Acoustic engineers can design a
soundproof room to stop sounds coming in from
outside, with materials that reduce or stop echoes
from the music being played.
b Engineers will try to reduce the noise inside
the railway station buildings, and also make sure
that people can hear loudspeakers used for making
announcements about trains.
Student Book
1: 7Le Comparing waves (Student Book)
1 In a transverse wave the particles vibrate/move
at right angles to the direction in which the wave is
travelling. In a longitudinal wave the motion of the
particles is along the same direction as the wave is
travelling.
2 up and down
3 a Some of it is transferred to the water and it
spreads out across the surface as waves.
b Drop a heavier stone (as it will have more
energy).
4 The duck furthest from the centre of the ripples;
as the ripples spread out there is less energy in
each section of wave, so the amplitude will get less.
5 Students can choose either type as the best
model but should provide reasons for their choice.
These could be: slinky is better as it can model a
longitudinal wave; water waves are better as they
spread out from a source but the wave in a slinky
only travels along the slinky.
6 Waves can be reflected by the cliffs, so they
could be coming from the direction of the sea and
from the direction of the cliffs. Some of the waves
may be bigger because if the peaks of a wave from
the sea and from the cliff occur together their effect
will add up and make a bigger wave.
7 Sound waves get smaller faster. Sound waves
spread out all around the source, but water waves
only spread out along the surface of the water.
The expanding sound waves form the surface of a
sphere and the area of this surface depends on the
radius squared. Expanding water waves form the
circumference of a circle, whose length depends
on the radius. So if the distance from a source is
doubled, the intensity of a sound wave will be a
quarter and the intensity of a water wave will be half.