3.3Chapter 3: Sound

Echoes — Alhussan Physics - Stage 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 4 2 quizzes

📚 Alhussan Physics - Stage 7 Hub / Topical Revision

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Lesson summary

3.3 Echoes — Sound Reflection, Sonar and Echolocation — Alhussan International Academy — Physics (Stages 7–9) notes: Describe how echoes are formed and how humans and animals use echoes, and calculate distance from the time for an echo to return.Echo = a reflection of sound, hear…

Time delay
Not a new sound
Large rooms
Reverberation
Reducing echoes
Ultrasound

Part 1 of 7What an echo is

Echo

Echo a reflection of sound, heard a short time after the original sound.

The sound wave spreads out and reflects off surfaces such as the walls of a cave.

Time delay

Time delay sound travels relatively slowly, so there is a time delay between a shout and the echo.

Not a new sound

Not a new sound an echo is the original sound reflected, not a new sound made by the wall.

Part 2 of 7Problems with echoes

Large rooms

Large rooms echoes can be a nuisance in cinemas and theatres,
- where sound reflects off all surfaces and echoes can last for several seconds, muddying the sound.

Reverberation

Reverberation the muddying of sound caused by many echoes lasting several seconds.

Reducing echoes

Reducing echoes cinema walls and ceilings are covered with soft, sound-absorbing materials.

Part 3 of 7Ultrasound

Ultrasound

Ultrasound sound with a frequency higher than 20 000 Hz, above the range of human hearing.

Use

Use humans and animals use sound that we cannot hear.

Why ultrasound

Why ultrasound beams of ultrasound are more focused than beams of audible sound,
- and they will not be confused with sounds made by people, animals or other boats.

Part 4 of 7Sonar

Sonar
- the word comes from sound navigation and ranging.
- Submarines use it to navigate underwater and ships use it to measure the depth of water.
- Fishermen use it to find fish.

A transmitter (an underwater loudspeaker) on the ship sends out pulses of ultrasound.

The waves travel through the water and reflect off objects such as rocks, fish or the sea bed.

The echoes return to the ship and are detected by underwater microphones (the receiver).

The device uses the time between sending and receiving to work out the depth of the water.

Part 5 of 7Calculating distance from an echo

Formula

Formula distance = speed × time.

Halve the time

Halve the time the measured time is for the journey there and back, so the time to the object is half of it.
distance = speed × (time ÷ 2).

Speeds of sound

Speeds of sound about 330 m/s in air and 1500 m/s in water.

Reason for halving

Reason for halving if the echo takes 1 second, the wave takes 0.5 s to reach the object and 0.5 s to come back.

Part 6 of 7Echolocation in animals

Echolocation

Echolocation finding the distance to an object by using echoes.

Dolphins and whales

Dolphins and whales they use echolocation more than sight, to find food or recognise family members in the dark or when the water is not clear.
The dolphin makes a series of clicking sounds.
The sound reflects off a fish.
The dolphin detects the echoes and uses the time to work out the location of the fish.

Bats

Bats they find the distance to objects using echolocation.

Distance

Distance sound travels much faster in water than in air, so dolphins and whales can also communicate over very long distances.
Dolphins can find food at greater distances than bats because sound travels faster and further in water.

Part 7 of 7Ultrasound scanning

Safety

Safety pregnant women are not given X-rays because they could harm both the fetus and the mother,
so doctors use ultrasound to check the development of the fetus.

Method

Method a transducer transmits ultrasound waves into the woman's body.
The waves are reflected by boundaries between soft tissue and by hard surfaces such as bone.
The transducer detects the echo and uses the time delay to calculate where the boundary is.

Image

Image by taking lots of pictures it is possible to build up a three-dimensional picture of the baby.

Key terms

Term	Meaning
Echo	a reflected sound heard a short time after the original sound.
Ultrasound	sound with a frequency higher than 20 000 Hz.
Sonar	sound navigation and ranging, using ultrasound pulses and echoes to find depth or objects underwater.
Echolocation	finding the position of an object by using echoes of sound.
Reverberation	the muddying of sound by echoes that last for several seconds.
Transducer	a device that converts energy from one form to another.