What is sound wave – Troubleinthepeace


Home New News High School Knowledge High School High School Grade 12 Physics 12 What is Sound Wave? Physical characteristics of sound waves and Exercises – Physics 12 lessons 10

Sound waves are the type of waves that we probably encounter most often in life, from the sound of mellow, vibrant music to loud, jarring sounds…

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So what are sound waves? How are sound waves transmitted, what are the physical characteristics of sound? What is the frequency of the sound that we hear, what is infrasound and infrasound? Let’s find out through the article below.

I. Sound waves and sound sources

1. What are sound waves?

– Definition: Sound waves are mechanical waves propagating through solid, solid, and gaseous media.

The frequency of the sound wave is the frequency of the sound.

2. Sound source

– An oscillating object emitting sound is a sound source.

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– The frequency of the sound emitted is equal to the frequency of vibration of the sound source

3. Audible, ultrasonic and infrasound Khoảng

– Audible sound (also called sound) is a sound with a frequency between 16 (Hz) and 20 000 (Hz).

– Ultrasound is sound with a frequency greater than 20 000 (Hz) and cannot be heard by the human ear, some species such as bats, dogs, pigs, etc. can “hear” ultrasound.

– Infrasound is the sound with a frequency less than 16 (Hz) and cannot be heard by the human ear, some species such as elephants, birds, pigeons, etc. can “hear” infrasound.

4. Sound transmission

a) Sound transmission medium

– Sound can be transmitted in solid, liquid and gaseous mediums; cannot propagate in a vacuum.

– Sound can hardly be transmitted through porous substances such as cotton, wool, etc., called soundproofing substances.

b) Speed ​​of sound

In each medium, sound travels at a definite, finite speed.

* Examples of Speed ​​of sound in some substances

Substance v(m/s) Air at 00C 331 Air at 250C 346 Hydrogen at 00C 1 280 Water, sea water at 150C 1 500 Iron 5 850 Aluminum 6 260

II. Physical characteristics of sound

1. Negative frequency

Sound frequency is one of the most important physical characteristics of sound

2. Sound intensity and sound intensity level

a) Sound intensity

• Sound intensity is the energy of a sound wave traveling through a unit area placed perpendicular to the direction of wave propagation per unit time.

– Sound intensity is denoted by: I; Unit: W/m2 (watts per square meter)

b) Sound intensity level

– Recipe:

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– Unit: B (ben); 1B = 10dB(decibels) or

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* Several levels of sound intensity

Sound source L(dB) Falling leaves, whispering 1 m away 10 Deserted garden, silent room 20 Soft music, house noise 40 Talking 1 m away 60 Street noise 80 Air jet at night take off 130

3. Basic tones and harmonics

• When an instrument emits a sound with frequency f0, that instrument always simultaneously emits a type of sound with frequencies: 2f0, 3f0, 4f0,… with different intensities:

The sound with frequency f0 is called the fundamental tone

• The tones with frequencies 2f0, 3f0, 4f0, etc. are called second, third, fourth harmonics, etc.

– The harmonics have different amplitudes, making the sound vibration graph of the instruments when emitting the same note is also different. This difference is distinguished by their timbre.

– The third physical characteristic of a sound is its vibrational graph.

III. Exercise on Sound Waves

* Lesson 1, page 55, Physics 12 textbook: Do infrasound and ultrasound have the same nature?

° Solution 1 page 55 Physics textbook 12:

– Infrasound and ultrasound have the same nature as mechanical waves, only differing in frequency.

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* Lesson 2, page 55, Physics 12 Textbook: What is sound wave?

° Solution 1 page 55 Physics textbook 12:

Sound waves are mechanical waves propagating through solid, liquid, or gaseous media.

* Lesson 3, page 55, Physics 12 Textbook: What is music?

° Solution to lesson 3, page 55, Physics 12 textbook:

Music is a sound with a definite frequency, usually emitted by musical instruments.

* Lesson 4, page 55, Physics 12 textbook: Of the three solid, liquid, and gaseous media, which medium travels the fastest and in which medium is the slowest?

° Solution 4 page 55 Physics textbook 12:

– In three media: solid, liquid, gas, sound travels fastest in solids and slowest is sound in air.

* Lesson 5, page 55, Physics 12 textbook: How is sound intensity measured?

° Solution for lesson 5, page 55, Physics 12 textbook:

– Sound intensity I at a point is a quantity measured by the amount of energy that a sound wave carries through a unit area placed at that point, perpendicular to the direction of wave propagation in a unit time.

– The unit of sound intensity is watts per square meter, denoted by: W/m2

* Lesson 6, page 55, Physics 12 Textbook: Select the correct answers. Ultrasound is sound:

A. has a high frequency

B. has great intensity

C. has a frequency above 20000Hz

D. propagates in any medium faster than sound

° Solution for lesson 6, page 55, Physics 12 textbook:

¤ Choose the answer: C. has a frequency above 20000Hz

Ultrasound waves: A sound wave with a frequency greater than 20000Hz that does not cause hearing sensation in humans.

* Lesson 7 page 55 Physics 12 Textbook: Select the correct answers. Sound intensity is measured by:

A. watts per square meter.

B. watt

C. newtons per square meter

D. newton per meter

° Solution to lesson 7 on page 55 of Physics 12 Textbook:

¤ Choose the answer: A.watt per square meter.

– Sound intensity I at a point is a quantity measured by the amount of energy that a sound wave carries through a unit area placed at that point, perpendicular to the direction of wave propagation in a unit time.

– The unit of sound intensity is watts per square meter, denoted by: W/m2

* Lesson 8 page 55 Physics 12 textbook: A sheet of steel oscillates with a period T = 80ms. Can the sound it emits be heard?

° Solution of lesson 8 page 55 Physics textbook 12:

¤ Problem for: T = 80(ms) = 80.10-3(s).

– We have:

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– We see: 12.5 (Hz) < 16 (Hz) is infrasound, so this sound we cannot hear.

* Lesson 9 page 55 Physics 12 textbook: An ultrasound has a frequency of 1MHz. Using Table 10.1 SGK, calculate the wavelength of this ultrasound in air at 0oC and in water at 15oC.

° Solution to lesson 9 page 55 Physics 12 textbook:

¤ Problem for: f = 1MHz = 106(Hz); tkk = 00C and water = 150C

– According to Table 10.1, the speed of sound in air at 0oC is vkk = 331 (m/s), in water at 15oC is vn = 1500 (m/s).

– We have, in air at 00C, the wavelength of ultrasound is:

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In water at 150C, the wavelength of ultrasound is:

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* Lesson 10, page 55, Physics 12 textbook: To measure the speed of sound in cast iron, French physicist Bio used a cast iron tube 951.25 meters long. One person hits one end of the cast iron pipe with a hammer, one person at the other end hears two knocks, one through the cast iron and the other through the air in the cast iron pipe; Those two hours are 2.5 seconds apart. Knowing the speed of sound in air is 340m/s, calculate the speed of sound in cast iron.

° Solution for lesson 10, page 55, Physics 12 textbook:

– Let v1, v2 be the speed of sound traveling in cast iron and in air, respectively, we have

– The time that the person hears the sound traveling in the cast iron is:

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The time taken by the person to hear the sound traveling through the air is:

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– According to the problem, we have: Δt = t2 – t1 = 2.5(s); s = 951.25m; v2 = 340(m/s).

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(Note: The speed of sound in cast iron is faster than that in air.)

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Hope the above article has helped you better understand about What is sound wave? physical characteristics of sound waves and can solve problems on sound waves. Any suggestions and questions, please leave a comment below the article for webgiaidap.com to recognize and support, wish you a good study.

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