G11 phy ch5 Power of sound Vid 1of3 En 20 21 1
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
🎓 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.
🔍 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
💡Energy
💡Acoustic Power
💡Amplitude
💡Threshold of Hearing
💡Threshold of Pain
💡Sound Intensity Level
💡Damped Wave
💡Absorbance Medium
💡Electroacoustic Converter
💡Acoustic Electric Converter
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
[Music]
my dear students in this video we're
going to study part 1 of chapter 5 sound
energy which is the last chapter of the
first unit waves
let us learn more about a sound wave
at the end of this chapter you will be
able to
and 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
in this video only the first objective
will be covered
before we start let's remember the main
points of the previous chapter
one sound is a longitudinal mechanical
wave produced by the vibration of an
object in a material medium
two
sound is fastest in solids
three loudspeaker is an electro acoustic
converter
four microphone is an acoustic electric
converter
five the audible range of a sound is
between 20 hertz and 20 thousand thirds
and some applications of ultra sound
waves are sonar echography and
exploration of fossils
sound is a wave that propagates in a
material medium
it carries energy known as sound energy
or acoustic energy
the energy transmitted to your ear
causes your eardrum to vibrate
this energy is expressed in joules
the abstract definition of the sound
energy is really obvious but what about
its practical one will it be obvious
also is that real
watch carefully and the judge
[Music]
so
as we have seen in this video that sound
energy can break a glass due to its
vibratory motion
every sound emitter for example a
loudspeaker provides energy to the
medium of perpetration
the acoustic power p of a transmitter is
the energy it provides to the
surrounding environment per unit of time
it is defined by p is equal energy
divided by the time
where the energy is expressed in joules
time in seconds and the power in what
in the case of a sinusoidal sound wave
the power is proportional to the square
of the amplitude
and it is given by p is equal to ka
squared if the amplitude that is from a
to a prime then b will be p prime such
that
b divided by p prime is equal to k a
squared divided by k a prime squared
which is equal to a divided by a prime
all squared
note
a wave is said to be damped if its
amplitude decreases that means its
energy decreases with time
a sound wave is damped in a so-called
absorbance medium where part of its
energy is transformed into thermal
energy due to friction between the
molecules of propagation
of the medium
let us now solve application number one
a sound source emits two times 10 to the
power 5 joules each minute the question
is to calculate the sound power emitted
by this source
using p is equal to e divided by t
it will give 2 times 10 to the power 5
joules divided by 1 times 60 seconds
which is 3.33 times 10 to the power 3
what
in application 2
we consider a sinusoidal wave of power p
and amplitude a
the question is to determine the new
power p prime if we double the amplitude
of this wave the initial power is given
by p is equal to k a squared
after doubling the amplitude the power
change to be p prime which is given by
p prime is equal to k a prime squared
but we know that a prime is equal to a
then my substitution b prime will give
4k a squared therefore p prime is equal
to 4p
if we want to use another method we have
to find the ratio between p and p prime
which will give ka squared divided by ka
prime squared
and when substituting a prime
by two a this ratio will give one over
four so we conclude that p prime is
equal to four p
[Music]
thank you for watching and please study
this video
[Music]
you
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