Topic 4: physics

Ultrasound

Sound waves above 20 KHz is called Ultrasound which humans ears can't detect. Ultrasound waves are partially reflected at a boundary between media. Partial reflection is when a wave is passed from one medium to another, some of the wave is reflected off the boundary between the two media and some is transmitted and refracted. 

So you can point a pulse of ultrasound at an object and if there are boundaries between one substance and another, the ultrasound gets reflected back. 

What is ultrasound used for? 

It is used to break down kidney stones which is then passed through urine and for body scans to detect gal stone, tumors or pregnancy. It is also used for sonar detection. 

When ultrasound is directed at a human body, the surface of different tissues inside the body due to partly reflect the ultrasound. The detector will receive the ultrasound echoes at different time depending on how deep inside the body the tissue surface are.

The detector produces electrical signals which are sent to a computer and then displayed on a screen as a picture. Ultrasound can be used safely to see an image of a developing baby inside the uterus during pregnancy.

With boats and submarines, they use sonar to detect objects in the water surrounding them. They emit waves of ultrasounds which reflects off of the objects e.g. boats, sea bed and marine animals. The boat detects the reflected waves when it arrives back at the boat. Computers time the delay between the emission of the wave and the detection of the wave which they then calculate how far the other objects are.

Animals such as bats use ultrasound to sense their way around their enviorment or to communicate with one another. Dolphins use echolocation by releasing beams of clicking sound (ultrasound) and listen for the echoes. They can decipher from this the size, shape, distance, speed, direction and internal structure (depends on the object)

Infra sound

Infra sound is sound waves with frequency less than 20Hz. They are used by…