Ultrasound

Learning Objectives

1. Describe the hearing range in humans (L5)

2.Explain what ultrasonic sound is (L6)

3.Recognise the uses of ultrasonic sound

Starter

ULTRASOUND

• Ultrasound is the name we give to sound that is too high pitched for humans to hear.

• The frequency or number of vibrations each second is so high that our ears will not detect the vibrations.

• The human ear does not perceive all frequencies equally. We hear sounds best at around 3,000 to 4,000Hz.

WHAT SOUNDS CAN WE HEAR?

• Humans can hear sounds at frequencies from about 20Hz to 20,000Hz. This is called the AUDIBLE RANGE.

• Humans don't hear all sounds. For example, we can't hear the sound a dog whistle makes, but dogs can hear that sound.

• Marine animals can often hear sounds that humans can't hear.

• The audible range for adults varies with age. As children, we may have an upper limit of nearly 30,000Hz but this decreases with age.

CHILD

20 – 30,000Hz

ADULT

20-20,000Hz

PENSIONER

20-15,000Hz

Hearing range for other animals.

• Bats can hear up to 120,000 Hz• Cats can hear up to 70,000 Hz• Dogs can hear up to 50,000 Hz• Humans can hear up to 20,000 Hz• Some insects can hear up to 15,000

Hz• Sound lower than 20 Hz is known as

infrasound.

Medicine• Ultrasound is used to scan organs

such as the heart, brain or liver without the need for surgery.

• Ultrasonic waves are used to build up an image of the developing baby in the mother’s womb. This enables the doctor to check the progress of a pregnancy.

Common use: Pregnancy scan.

• Kidney stones are broken up without the need for surgery using ultrasound. The high-frequency wave vibrations are directed at the stones which causes them to vibrate and break up. They are then passed painlessly from the body.

Dentistry

• Ultrasound is used to remove plaque from teeth.

The high frequency wave vibrations cause the plaque to vibrate so much that it breaks up and falls off.

Cleaning• A similar effect is used to clean many

different types of objects, especially surgical instruments.

• The objects are immersed in a liquid and ultrasonic waves are directed through it.

• The high frequency waves create a ‘scrubbing’ action in the fluid and any unwanted material is removed from the objects.

• Ultrasound is also used to clean delicate machinery without the need to dismantle it.

Cracks• Ultrasound reflects off cracks in metals,

so can be used to check for faults in aircraft and in underground pipes.

Sound Waves.

Learning Objectives

Explain what a sound wave is (L4)

Recognise the difference between a compression and a rarefaction (L5/6)

Understand how a loudspeaker produces sound

Compressions and rarefractions

• A pulse, or wave, of energy passes down the spring.

• This is called a push wave. The energy passes through the spring.

• When a wave is passing along a point at any given point, its coils are pushed together compressions and those that are stretched out are called rarefactions.

RarefractionCompression

Energy Transport. Energy Transport.

• Sound waves are …………………………… waves.

• When someone speaks, the air particles vibrate as a longitudinal wave and so ………………………. and ………………….. are formed in the air.