G11 phy ch5 Power of sound Vid 1of3 En 20 21 1

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23 Aug 202205:57

Summary

TLDRIn this educational video, students delve into the final chapter of the first unit on waves, focusing on sound energy. They learn to calculate the power of a sound emitted by a point source and the sound intensity at a point. The video covers the definition of sound energy, its practical implications, and how it can break a glass. It also explains the concept of acoustic power, its relation to amplitude, and how it changes with amplitude adjustments. The tutorial includes solving practical problems to reinforce understanding.

Takeaways

  • 📚 This video is part of a series studying chapter 5 on sound energy, focusing on the first objective of determining the power of a sound emitted by a point sound source.
  • 🎵 Sound is a longitudinal mechanical wave that carries energy known as sound energy or acoustic energy, which is expressed in joules.
  • 🔊 The audible range of sound is between 20 hertz and 20,000 hertz, with applications of ultrasound waves including sonar, echography, and exploration of fossils.
  • 🔧 A loudspeaker is an electro-acoustic converter, while a microphone is an acoustic-electric converter.
  • ⏱️ Acoustic power (P) is defined as the energy provided to the surrounding environment per unit of time, calculated as P = energy / time.
  • 🌊 In a sinusoidal sound wave, power is proportional to the square of the amplitude, expressed as P = kA^2, where k is a constant.
  • 📉 A damped wave is one where amplitude decreases over time, indicating a reduction in energy, often due to energy being transformed into thermal energy in an absorbent medium.
  • 🔄 If the amplitude of a sound wave is doubled, the power increases by a factor of four, as shown by the formula P' = 4P when A' = 2A.
  • 📝 The video provides practical examples and applications to help students understand the abstract and practical definitions of sound energy.
  • 👨‍🏫 The instructor encourages students to watch the video and study the material to gain a deeper understanding of sound energy concepts.

Q & A

  • What is the main focus of the video?

    -The main focus of the video is to study part 1 of chapter 5 on sound energy, which is the last chapter of the first unit on waves.

  • What are the objectives that students will be able to achieve by the end of the chapter?

    -By the end of the chapter, students will be able to determine the power of a sound emitted by a point sound source, determine the sound intensity at a point, define the threshold of hearing and the threshold of pain, and determine the sound intensity level at a point.

  • Which objective is covered in the video?

    -In the video, only the first objective, which is to determine the power of a sound emitted by a point sound source, is covered.

  • What is the definition of sound?

    -Sound is defined as a longitudinal mechanical wave produced by the vibration of an object in a material medium.

  • How does the speed of sound vary in different mediums?

    -Sound travels fastest in solids, slower in liquids, and slowest in gases.

  • What is the audible range of sound for humans?

    -The audible range of sound for humans is between 20 hertz and 20,000 hertz.

  • What is sound energy and how is it expressed?

    -Sound energy is the energy transmitted by sound waves as they propagate through a medium. It is expressed in joules.

  • How is the acoustic power of a transmitter defined?

    -The acoustic power P of a transmitter is the energy it provides to the surrounding environment per unit of time, defined by P = E / t, where E is energy in joules, t is time in seconds, and P is power.

  • What happens to a sound wave in an absorbent medium?

    -In an absorbent medium, a sound wave is damped, meaning its amplitude and energy decrease with time, as part of its energy is transformed into thermal energy due to friction between the molecules of the medium.

  • If a sound source emits 2 x 10^5 joules each minute, what is the sound power emitted by this source?

    -The sound power emitted by the source is 3.33 x 10^3 watts, calculated using the formula P = E / t, where E = 2 x 10^5 joules and t = 60 seconds.

  • If the amplitude of a sinusoidal wave is doubled, what happens to its power?

    -If the amplitude of a sinusoidal wave is doubled, the power increases by a factor of four, as the power is proportional to the square of the amplitude.

Outlines

00:00

🎓 Introduction to Sound Energy and Power

This paragraph introduces the topic of sound energy and power as part of a physics lesson. The instructor begins by setting the context that this is the last chapter of the first unit on waves. The chapter's objectives include understanding sound waves, determining the power of a sound emitted by a point source, defining sound intensity at a point, and understanding the thresholds of hearing and pain. The instructor also aims to teach how to determine the sound intensity level. The video will only cover the first objective. A brief review of the previous chapter is provided, highlighting that sound is a longitudinal mechanical wave, fastest in solids, and mentioning devices like loudspeakers and microphones that convert between sound and electrical energy. The audible range of sound is also mentioned, along with applications of ultrasound like sonar and medical imaging. The instructor then explains that sound carries energy, which can cause the eardrum to vibrate, and this energy is measured in joules. The practical demonstration of sound energy is hinted at with a suggestion to watch carefully.

05:03

🔍 Calculations of Sound Power and Amplification

In this paragraph, the focus shifts to practical calculations related to sound power. The instructor explains that the acoustic power (P) of a transmitter is the energy it provides to the surrounding environment per unit time, mathematically defined as P = energy / time. The energy is in joules, time in seconds, and power in watts. For a sinusoidal sound wave, power is proportional to the square of the amplitude. The instructor provides a formula for calculating power based on amplitude and a constant (k). An example is given where a sound source emits a certain amount of energy per minute, and the instructor demonstrates how to calculate the sound power using the formula. The concept of a damped wave is introduced, explaining that it's a wave where amplitude decreases over time, leading to a decrease in energy. This is particularly true in absorbent media where energy is transformed into thermal energy due to molecular friction. The paragraph concludes with a problem-solving example where the power of a sinusoidal wave is calculated after the amplitude is doubled, demonstrating the relationship between power and amplitude.

Mindmap

Keywords

💡Sound Wave

A sound wave is a longitudinal mechanical wave that is produced by the vibration of an object in a material medium. In the context of the video, understanding sound waves is fundamental as it discusses how these waves carry energy and can be manipulated. The video script mentions that sound is a wave that propagates in a material medium, carrying energy known as sound energy or acoustic energy.

💡Energy

Energy, in the context of the video, refers to the sound energy or acoustic energy that is transmitted through a medium by a sound wave. It is the power behind the vibrations that cause our eardrums to vibrate. The video script illustrates this by explaining that the energy is expressed in joules and is provided to the surrounding environment by a sound emitter.

💡Acoustic Power

Acoustic power is the energy provided by a sound source to its surrounding environment per unit of time. It is a crucial concept in the video as it defines how much energy a sound source emits. The script uses the formula 'P = E / t' to calculate the sound power, where P is the power, E is the energy in joules, and t is the time in seconds.

💡Amplitude

Amplitude in the video refers to the maximum displacement of a point on a wave from its equilibrium position. It is related to the intensity of the sound. The script explains that for a sinusoidal sound wave, the power is proportional to the square of the amplitude, indicating that a larger amplitude results in greater sound power.

💡Threshold of Hearing

The threshold of hearing is the minimum sound intensity level that can be heard by the human ear. The video mentions this concept as part of the objectives, suggesting that students will learn to define it and understand its importance in the study of sound.

💡Threshold of Pain

The threshold of pain is the highest level of sound intensity that a person can tolerate before experiencing pain. This concept is also mentioned as an objective in the video, indicating its relevance in understanding the limits of human auditory perception.

💡Sound Intensity Level

Sound intensity level is a measure of the power of a sound relative to a reference level. The video script discusses how to determine the sound intensity level at a point, which is an important aspect of understanding how loud a sound is perceived to be.

💡Damped Wave

A damped wave is one whose amplitude decreases over time, meaning its energy decreases as it propagates. The video script explains that a sound wave is damped in an absorbent medium where part of its energy is transformed into thermal energy due to friction between the molecules of the medium.

💡Absorbance Medium

An absorbance medium is a material that absorbs part of the energy from a sound wave, causing it to lose amplitude and become damped. The video uses this term to describe environments where sound energy is not just transmitted but also transformed into other forms of energy, such as heat.

💡Electroacoustic Converter

An electroacoustic converter, such as a loudspeaker, is a device that converts electrical signals into sound waves. The video script mentions this as a point of review from the previous chapter, highlighting the role of such devices in the generation and manipulation of sound.

💡Acoustic Electric Converter

An acoustic electric converter, like a microphone, is a device that converts sound waves into electrical signals. This concept is also reviewed in the video script, emphasizing the reverse process of the electroacoustic converter and its importance in sound recording and transmission.

Highlights

Studying part 1 of chapter 5 on sound energy, the last chapter of the first unit on waves.

Objective to determine the power of a sound emitted by a point sound source.

Learning to determine the sound intensity at a point.

Defining the threshold of hearing and the threshold of pain.

Determining the sound intensity level at a point.

Reviewing that sound is a longitudinal mechanical wave produced by object vibrations.

Sound travels fastest in solids.

Understanding a loudspeaker as an electro-acoustic converter.

Recognizing a microphone as an acoustic-electric converter.

The audible range of sound is between 20 Hz and 20 kHz.

Applications of ultrasound waves include sonar, echography, and fossil exploration.

Sound energy can break a glass due to its vibratory motion.

Acoustic power P is the energy provided to the environment per unit time.

In sinusoidal sound waves, power is proportional to the square of the amplitude.

Damped waves have decreasing amplitude and energy over time.

Sound waves are damped in absorbent media, where energy is transformed into thermal energy.

Calculating sound power emitted by a source using the formula P = E/t.

Doubling the amplitude of a sinusoidal wave results in a power increase by a factor of four.

Thank you for watching and encouragement to study the video.

Transcripts

play00:00

[Music]

play00:11

my dear students in this video we're

play00:13

going to study part 1 of chapter 5 sound

play00:16

energy which is the last chapter of the

play00:19

first unit waves

play00:21

let us learn more about a sound wave

play00:25

at the end of this chapter you will be

play00:27

able to

play00:29

and determine the power of a sound

play00:31

emitted by a point sound source

play00:34

determine the sound intensity at a point

play00:37

define the threshold of hearing and the

play00:39

threshold of pain

play00:41

and determine the sound intensity level

play00:43

at a point

play00:44

in this video only the first objective

play00:47

will be covered

play00:49

before we start let's remember the main

play00:52

points of the previous chapter

play00:54

one sound is a longitudinal mechanical

play00:57

wave produced by the vibration of an

play00:59

object in a material medium

play01:02

two

play01:03

sound is fastest in solids

play01:06

three loudspeaker is an electro acoustic

play01:09

converter

play01:10

four microphone is an acoustic electric

play01:14

converter

play01:15

five the audible range of a sound is

play01:18

between 20 hertz and 20 thousand thirds

play01:22

and some applications of ultra sound

play01:24

waves are sonar echography and

play01:27

exploration of fossils

play01:31

sound is a wave that propagates in a

play01:33

material medium

play01:35

it carries energy known as sound energy

play01:38

or acoustic energy

play01:41

the energy transmitted to your ear

play01:43

causes your eardrum to vibrate

play01:46

this energy is expressed in joules

play01:51

the abstract definition of the sound

play01:53

energy is really obvious but what about

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its practical one will it be obvious

play01:59

also is that real

play02:01

watch carefully and the judge

play02:06

[Music]

play02:13

so

play02:29

as we have seen in this video that sound

play02:32

energy can break a glass due to its

play02:35

vibratory motion

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every sound emitter for example a

play02:40

loudspeaker provides energy to the

play02:43

medium of perpetration

play02:45

the acoustic power p of a transmitter is

play02:48

the energy it provides to the

play02:49

surrounding environment per unit of time

play02:53

it is defined by p is equal energy

play02:56

divided by the time

play02:58

where the energy is expressed in joules

play03:01

time in seconds and the power in what

play03:05

in the case of a sinusoidal sound wave

play03:08

the power is proportional to the square

play03:10

of the amplitude

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and it is given by p is equal to ka

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squared if the amplitude that is from a

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to a prime then b will be p prime such

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that

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b divided by p prime is equal to k a

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squared divided by k a prime squared

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which is equal to a divided by a prime

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all squared

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note

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a wave is said to be damped if its

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amplitude decreases that means its

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energy decreases with time

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a sound wave is damped in a so-called

play03:50

absorbance medium where part of its

play03:53

energy is transformed into thermal

play03:55

energy due to friction between the

play03:58

molecules of propagation

play04:00

of the medium

play04:02

let us now solve application number one

play04:06

a sound source emits two times 10 to the

play04:08

power 5 joules each minute the question

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is to calculate the sound power emitted

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by this source

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using p is equal to e divided by t

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it will give 2 times 10 to the power 5

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joules divided by 1 times 60 seconds

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which is 3.33 times 10 to the power 3

play04:28

what

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in application 2

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we consider a sinusoidal wave of power p

play04:35

and amplitude a

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the question is to determine the new

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power p prime if we double the amplitude

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of this wave the initial power is given

play04:47

by p is equal to k a squared

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after doubling the amplitude the power

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change to be p prime which is given by

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p prime is equal to k a prime squared

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but we know that a prime is equal to a

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then my substitution b prime will give

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4k a squared therefore p prime is equal

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to 4p

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if we want to use another method we have

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to find the ratio between p and p prime

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which will give ka squared divided by ka

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prime squared

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and when substituting a prime

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by two a this ratio will give one over

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four so we conclude that p prime is

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equal to four p

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[Music]

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thank you for watching and please study

play05:46

this video

play05:47

[Music]

play05:56

you

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الوسوم ذات الصلة
Sound EnergyAcousticsEducational VideoWave MechanicsPhysics ChapterMechanical WavesAudio PowerSound IntensityEducational ContentScience Learning
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