6.1.u = 6.1.x Human hearing and ultrasound

6 parts of the ear

• Pinna (outer ear)

• Ear canal

• Ear drum

• Ossicles (tiny bones)

• Cochlea

• Auditory nerve

What does the pinna do?

It’s the outer ear, helping to channel sound waves into our heads

What does the ear canal do?

It’s a tube down which sound waves can pass

What does the ear drum do?

It’s a thin membrane, where vibrations are passed into the ear bones. Sound waves in the air make this vibrate

What does the ossicle do?

They are 3 tiny bones, passing vibrations onto the cochlea in order to amplify vibrations

What does the cochlea do?

It’s a membrane with hair cells that detect vibrations. It’s also filled with liquid, (affects balance) Vibrations are turned into nerve impulses. Contains a membrane thicker at one end than the other

What do the auditory nerves do?

It’s made up of neurons , passing impulses to the brain

How does sound travel?

• Sound requires a medium eg. gas, liquid, solid

• Energy is transferred by neighbouring particles

• In solids, particles are closer together so sound will travel faster

How can we prove that sound travels through a medium?

Using a vaccum pump to suck air out, of a glass bell jar removing particles so there are no air molecules to vibrate . No medium.

What is the human hearing range?

20Hz to 20,000Hz

Frequencies less than 20Hz are ?

Infrasound

Frequencies more than 20,000Hz are ?

Ultrasound

What is ultrasound?

• 20,000Hz<

• Cannot be heard by humans

• many animals such as bats and dolphins use ultrasound to communicate or find prey.

How do bats use ultrasound?

Bats emit pulses of ultrasound, things around them reflect the waves so bats detect these echos.

What is sonar?

• Used to map the seabed or find fish

• Emitted from a boat to the seabed and reflected back to the boat

• Time for signal to get back must be halved as it bounces back

Why do we use ultrasound instead of light for sonar?

Light doesn’t travel very far through water before it gets scattered and refracted therefore it won’t get very far.

What are ultrasound scanners

• Used for prenatal scanners for a baby in the womb

• Imaging organs in the body to find damage

• Electronic device called transducer placed on a bodily surface, a control system + display. Transducers produce and detect sets or pulses of ultrasound waves.

What are the advantages of ultrasound scanners?

• Reflected at boundaries between different types of tissue, so can be used to scan organs + other soft tissues without damage.

• Non - ionising radiation, doesn’t have enough energy to remove an electron to ionise an atom or molecule. So it’s harmless when used.

How does foetal scanning work?

1. Ultrasound pules are sent in to the woman’s body

2. Jelly is used to make sure the ultrasound is not reflected by her skin

3. Some of the ultrasound is reflects each time, it meats different materials such as bon, muscle or fluid

4. The scanner detects the echoes, and measure the time the sound has taken

5. It uses the times to calculate the distance to the different parts of the foetus and builds up and image.

What affects ultrasound scanners?

• The further away a boundary is from the transmitter, the longer a reflected wave takes to return

How can we use an oscilloscope?

Measures time take by a wave to travel from the transmitter at the surface to + from the boundary that reflected it

Depth of boundary below surface = 

½ speed of ultrasound x time

Distance travelled by wave =

Speed of ultrasounds x time take for wave to reflect back