ultrasound

what is ultrasound

Ultrasound is sound that has a wave frequency higher than the human ear can detect. It includes all sound with wave frequencies higher than 20,000 waves per second, or 20,000 hertz (Hz). Although we cant hear ultrasound, it is very useful to humans and some other animals. Uses of ultrasound include echolocation, sonar, and ultrasonography.

echolocation

Animals such as bats and dolphins send out ultrasound waves and use their echoes, or reflected waves, to identify the locations of objects they cannot see. This is called echolocation. Animals use echolocation to find prey and avoid running into objects in the dark. You can see in the Figure 1.1 how a bat uses echolocation to find insect prey.

sonar

Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as submarines. Thats how the ship pictured in the Figure 1.2 is using it. A sonar device is both a sender and a receiver. It sends out ultrasound waves and detects the waves after they reflect from underwater objects. The distance to underwater objects can be calculated from the known speed of sound in water and the time it takes for the sound waves to travel to the object. The equation for distance traveled when speed and time are known is: Distance = Speed Time Consider the ship and submarine pictured in the Figure 1.2. If an ultrasound wave travels from the ship to the submarine and back again in 2 seconds, what is the distance from the ship to the submarine? The sound wave travels from the ship to the submarine in just 1 second, or half the time it takes to make the round trip. The speed of sound waves through ocean water is 1437 m/s. Therefore, the distance from the ship to the submarine is: Q: Now assume that the sonar device on the ship sends an ultrasound wave to the bottom of the water. If the sound wave is reflected back to the device in 4 seconds, how deep is the water? A: The time it takes the wave to reach the bottom is 2 seconds. So the distance from the ship to the bottom of the water is: Distance = 1437 m/s 2 s = 2874 m

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ultrasonography

Another use of ultrasound is to see inside the human body. This use of ultrasound is called ultrasonography. Harmless ultrasound waves are sent inside the body, and the reflected waves are used to create an image on a screen. This technology is used to examine internal organs and unborn babies without risk to the patient. You can see a doctor using ultrasound in the Figure 1.3.

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instructional diagrams

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questions

some animals use echolocation to find prey.

-->  a. true

b. false

sonar is used to determine the

a) speed of motor vehicles.

-->  b) distance to underwater objects.

c) location of approaching storms.

d) all of the above

you can calculate distance from speed and time with the equation

a) distance = speed/time.

b) distance = time/speed.

-->  c) distance = speed x time.

d) none of the above

the speed of sound waves through ocean water is 1437 m/s. assume that ultrasound waves take 2 seconds to travel from a sonar device on a ship to the bottom of the water and back to the ship again. how deep is the water?

a) 2874 m

-->  b) 1437 m

c) 718 m

d) none of the above

the use of reflected ultrasound waves to create images of organs inside the body is called ultrasonography.

-->  a. true

b. false

diagram questions

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