"Ultrasound and Infrasound" The World of Sound PPT Courseware 3

Description

"Ultrasound and Infrasound" The World of Sound PPT Courseware 3

【Experience】Try it and listen to it

Activity 1: Use the same force to move different plastic rulers, as shown in Figure A, which is 20cm long.

Student ruler, as shown in Figure B, moves a 1m long plastic ruler.

Activity 2: As shown in the picture, take a cylindrical food can, cut a round hole on one end, remove the bottom surface and cover it with a rubber film on the other end, and tie it tightly with a rubber band. Light the candle on the table. When the candle flame stops shaking, point the opening of the cylinder toward the candle and tap the rubber membrane with your hand.

(1) In activity 1, when the plastic ruler with a length of 20cm is moved, the vibration frequency of the ruler is about _____Hz. _____ (optional "can" or "cannot") is heard. When the plastic ruler with a length of 1m is moved, the vibration frequency of the ruler is about _____Hz. _____Hz, _____ (optional "can" or "cannot") hear the sound.

(2) When you tap the rubber film with your hand, the candle flame will _____.

Tips: (1) 30, Able, 2~5, Unable (2) Shake

pre-study questions

1. What is ultrasound? What is infrasound?

2. What are the applications of ultrasound? What are the hazards of infrasound?

Study 1 Ultrasound and Noise

Combined with "experience", think about the following questions:

1. Under normal circumstances, can the human ear hear sounds in all frequency ranges?

Tip: Human ears can only hear sounds with frequencies between 20 and 20,000 Hz, and sounds outside this frequency range cannot be heard by human ears.

Reference answer: No

2. How are the frequency ranges of ultrasound and infrasound divided?

Reference answer: Sound above 20 000Hz is called ultrasound, and sound below 20Hz is called infrasound.

3. In activity 1, when you turn the plastic ruler, you can hear the vibrating sound of the short plastic ruler but not the long plastic ruler. The reason is that the vibration frequency of the long plastic ruler is lower than _____Hz. Inaudible to human ears. What conditions should be met for the human ear to hear sound?

Tip: From Activity 1, we can see that the short plastic ruler vibrates faster, with a frequency between 20 and 20,000 Hz, and the sound it emits can be heard by human ears; the long plastic ruler vibrates slowly, with a frequency of about 2 to 5 Hz, which is lower than human hearing. The frequency range is inaudible to the human ear; the answer comes from the characteristics of sound propagation and the human ear itself.

Reference answer: 20 The conditions for the human ear to hear sound: (1) There is a sounding object that is the sound source; (2) The sound transmission medium; (3) The vibration frequency of the sounding object is between 20 and 20000Hz; (4) Must There is a certain loudness; (5) The human auditory system is intact.

Study 2 Ultrasound

1. Inspired by bats’ use of ultrasonic navigation, what instruments have people made? What are its applications?

Reference answer: Inspired by the use of ultrasonic navigation by bats, sonar was developed to detect the depth of the seabed, reefs, fish schools, and the location of submarines.

2. What are the characteristics of ultrasound? What are its specific applications?

Tip: Characteristics of ultrasound: ① good directionality, long propagation distance, ② strong penetrating ability, ③ strong breaking ability; specific applications: ① sonar, ② ultrasonic diagnostic instrument, ultrasonic metal flaw detector, ③ water The oil mixes and destroys the bacterial structure.

Reference answer: Good directionality, strong penetration and crushing capabilities; sonar, ultrasonic diagnostic instrument, ultrasonic metal flaw detector, water and oil mixing, destroying bacterial structure.

3. To use sonar to measure the depth of the seafloor, you need to know _____________, measure ________, and use the formula _______ to calculate.

Tip: Using sonar to measure the depth of the seafloor is actually to measure the distance from the point where the ultrasound is emitted to the reflecting surface. You need to know the propagation speed of ultrasound in seawater, measure the time it takes for the ultrasound wave to go from the sea surface to the seafloor and back to the sea surface, and calculate the distance from where the ultrasound wave travels. The time from the sea surface to the bottom of the sea, and then use the formula s=vt to find the depth of the bottom of the sea.

Reference answer: The propagation speed of ultrasound in seawater. The time for ultrasonic waves to travel from the sea surface to the bottom of the sea and back to the sea surface s=vt

Knowledge summary

1. Ultrasound

1. Definition: Sound of frequency __________.

2. Features: Frequency ___, penetrating ability, "breaking" ability ___, good transmission time.

3. Application: widely used in _____, _____ and ________.

2. Infrasound

1.Definition: Sound with frequency _______.

2. Characteristics: Frequency___, destructive power___.

3. Hazards: Infrasound waves with energy ___ are very destructive to machinery, human bodies and buildings.

4. Produce: ______, _____, storm, ______, missile launch, etc.

Test Points Application of Ultrasound and Infrasound Waves

[Typical example] (2011 Mianyang High School Entrance Examination) The following uses the reflection of ultrasonic waves to obtain information ()

A. Elephants’ “vocal” communication

B. "Echo" positioning of bats

C. Surgeon’s “ultrasound” removal of stones for stone patients

D. Standing in the center of the Temple of Heaven and speaking, your voice will feel particularly loud.

[Idea Guide] Clarify the scope of ultrasound and the applications of using ultrasound to obtain information, such as echolocation, B-ultrasound, etc.

【Exquisite analysis】Choose B. Because the "voice" of elephants is a kind of infrasound wave, humans cannot hear the sounds of communication between elephants, but elephants can hear and communicate with each other. Bats use ultrasonic reflection to obtain information. Surgeons use ultrasonic energy to expel stones in stone patients. When we stand in the center of the Temple of Heaven and speak, the sound spreads out and is reflected back by the surrounding tall buildings. What we hear is a mixture of echo and original sound, so the sound we hear is loud; human speech does not belong to ultrasonic waves. So choose B.

1. As shown in the picture, people use sonar to detect the location of fish schools, mainly using sonar ()

A.Electromagnetic waves B.Microwaves

C. Ultrasound D. Infrasound

[Analysis] Choose C. This question examines the application of sonar. Sonar uses ultrasonic echolocation to detect the location of fish schools.

2. After testing with an ultrasonic flaw detector, the Three Gorges Dam body has no structural cracks, creating a miracle in the history of human water conservancy construction. The ultrasonic waves emitted by the flaw detector cannot be heard by human ears because of the ()

A. The speed is too fast B. The loudness is too low

C. Frequency is too high D. Frequency is too low

[Analysis] Choose C. This question examines the characteristics of ultrasound. The characteristic of ultrasonic waves is high frequency rather than fast propagation speed, so choose C.

3. Which of the following statements is correct ()

A. Human ears cannot hear ultrasonic and infrasound waves, but some animals can hear them.

B. Infrasound waves are harmful to human beings but not beneficial at all.

C. By monitoring ultrasonic waves, volcanic eruptions can be monitored

D. The germination period of seeds treated with ultrasonic waves will be delayed and the growth period will be extended.

[Analysis] Choose A. This question examines the application of ultrasound and infrasound. People's hearing of high and low sounds has certain limits. The frequency range of sounds that people can hear is about 20Hz to 20000Hz. Ultrasound has the characteristics of good directionality, strong penetrating ability, and easy to obtain relatively concentrated sound energy, so it has a wide range of applications. Infrasound is generated in natural disasters, and people predict natural disasters through the study of infrasound.

Find out where you tend to go wrong?

Someone sends ultrasonic waves to the moon to measure the distance from the moon to the earth. Can he measure it? If it can be measured, please state the measurement method. If not, please explain the reason.

[Students’ own answers]

able. You need to know the propagation speed of ultrasonic waves in the air, measure the time it takes for the ultrasonic waves to travel from the ground to the moon and back to the ground, and then use the formula s=vt to find the distance.

[Teacher Comments]

The mistake is to ignore that ultrasonic waves cannot propagate in a vacuum.

【Standard Answer】

cannot. There is a vacuum between the Earth and the Moon, and ultrasound cannot pass through it.

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Update Time: 2024-12-09

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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