Infrasound and Ultrasound

Question 1

(2) Describe how infrasound differs from ultrasound.

Answer 1

• A difference in f or λ
(however described) (1)

This difference correctly qualified by
one of
• Relationship to each other
(1)
• Relationship to audible sound
(1)
• Frequency or wavelength
data (1)

Question 2

(1) Which of the following statements is the reason that people cannot hear infrasound?

Answer 2

the frequency of infrasound is

too low

Question 3

(3) Elephant A emits an infrasound call.
When elephant B hears the infrasound, it calls back.
Elephant A hears the answering call from elephant B.
The speed of infrasound is 340 m/s.
Show that the minimum time for elephant A to call and hear an answer from
elephant B is about 15 s.

Answer 3

transposition (1)
t = distance ÷ speed
substitution (1)
 (2 x )2500 ÷ 340
evaluation (1)
14.7 (s)

Question 4

(1) An elephant’s infrasound call has a range of 4000 m.
Each infrasound call lasts between 2 s and 10 s.
Each elephant usually waits about 30 s before it calls again.
Suggest a reason why elephants wait 30 s before calling again.

Answer 4

idea of a conversation (1)
• (4000 m is) a longer
distance taking a longer
time (to reach other
elephant) (1)
• time needed for waves to
travel is about 24 s (1)
• time gap between calls
(sufficient) for elephant to
hear a reply (1)
• call lasts long enough to be
identified by other elephants
(OWTTE) (1)

Question 5

(2) Describe a use of infrasound that does not involve animals

Answer 5

detecting/ locating/
monitoring (infrasound) (1)
• volcanic eruptions /
underground explosions /
earthquakes /nuclear
explosions / meteor strikes
(1)

Question 6

(1) Ultrasound is used for

Answer 6

communication between animals

Question 7

(2) Explain why ultrasound rather than X-rays are used for foetal scanning.

Answer 7

{X- rays are / ultrasound
is not} dangerous (1)
• (because X-rays) can
{damage / harm} {tissue
/ DNA} OR
mutate cells
OR
reverse argument for
ultrasound (1)

Question 8

(1) An ultrasound wave vibrate

State the frequency of the wave.s 30 000 times a second.

Answer 8

30 000 Hz / hertz

Question 9

(2) Describe the motion of particles in a material when this ultrasound wave
passes through.

Answer 9

particles {vibrate / oscillate} (1)
(move) in the {same direction as
/ parallel to the direction } the
wave travels (1)

Question 10

(6) Explain how sonar is used by deep sea fishermen to detect the depth of a shoal of
fish below the surface of the sea.

Answer 10

• sonar is ultrasound
• travels through water at the speed of sound (1500 m/s)
• ultrasound signal generated in the ship
• signal emitted from the bottom of the ship
• signal travels down through the water
• strikes shoal of fish
• signal reflected by fish
• reflected signal detected on the ship
• time between emission and detection measured
• either time halved and depth of fish calculated /or
distance wave travelled calculated and halved to give
depth of fish
• calculation done using x = v x t
• comparison of depths of fish and of seabed

Question 11

(2) Some people claim that animals can detect an earthquake before people are
aware of it.
Suggest an explanation for this.

Answer 11

Infrasound (1)
some animals can hear waves
below human frequency range /
20 Hz (1)
they could hear P waves arriving
before the (stronger) S waves
arrive (1)