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

Summary

In 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.