NCERT Solutions for Class 9 Science Chapter 12 - Sound

 

NCERT Solutions for Class 9 Science Chapter 12 - Sound

Section 12.1: What is Sound?

  • Q1. What is a sound wave? Answer: A sound wave is a mechanical wave that propagates through a medium (solid, liquid, or gas) by the vibration of particles in that medium. It requires a medium to travel and cannot travel through a vacuum.

Section 12.2: How Sound is Produced?

  • Q2. How is sound produced? Answer: Sound is produced when a body vibrates. These vibrations create compressions and rarefactions in the surrounding medium (usually air). These vibrations cause the particles of the medium to move and transmit the sound energy to the next particles.

Section 12.3: Propagation of Sound

  • Q3. How does sound travel through different media? Answer: Sound can travel through solids, liquids, and gases. The speed of sound is fastest in solids, slower in liquids, and slowest in gases. This is because the particles in solids are tightly packed, facilitating faster transmission of sound waves.

  • Q4. Why does sound travel faster in water than in air? Answer: Sound travels faster in water than in air because the particles in water are closer together than in air, allowing the vibrations to be transmitted more efficiently.

Section 12.4: Characteristics of Sound

  • Q5. What are the characteristics of sound? Answer: The main characteristics of sound are:
    1. Pitch - It determines the frequency of the sound wave. High-pitched sounds have high frequency, and low-pitched sounds have low frequency.
    2. Loudness - It refers to the amplitude of the sound wave. Larger the amplitude, the louder the sound.
    3. Quality (Timbre) - It differentiates between sounds of the same pitch and loudness. It depends on the waveform and harmonic content of the sound.

Section 12.5: Reflection of Sound

  • Q6. What is the reflection of sound? Answer: The reflection of sound occurs when sound waves bounce off a surface. This is the principle behind echoes. The angle at which the sound strikes a surface is equal to the angle at which it is reflected.

Section 12.6: Hearing and its Range

  • Q7. What is the range of hearing for humans? Answer: Humans can hear sounds in the frequency range of 20 Hz to 20,000 Hz. This range can vary with age, and it decreases as people grow older.

  • Q8. What is an echo? Answer: An echo is a reflected sound wave that returns to the listener after bouncing off a surface. It can be heard when the reflected sound reaches the listener after a certain time interval.

Section 12.7: Applications of Reflection of Sound

  • Q9. Mention some applications of the reflection of sound. Answer: Some applications of the reflection of sound include:
    • Echolocation in animals (bats, dolphins) to detect prey and navigate.
    • Sonar used in submarines to detect underwater objects.
    • Reverberation in concert halls to enhance sound quality.
    • Ultrasound in medical imaging.

Section 12.8: Speed of Sound

  • Q10. What factors affect the speed of sound? Answer: The speed of sound depends on the medium through which it travels and factors such as:
    • Temperature (sound travels faster in warmer temperatures).
    • Density of the medium (sound travels slower in denser media).
    • Elasticity (sound travels faster in more elastic media).

Comments

Post a Comment

Popular posts from this blog

Anna did what he had to do; what you will do to continue?

Image
Finally, Epic hungerstrike of Anna Hazaree has come to an end, raising hopes in the hearts of masses and leaving veteran bloodsucking politicians pucker- liped, with UPA government bowing to all his major demans over Lokpal Bill. However, developments, erupting in the recent days followed by end of his hunderstike, seems to be conspiring to blow up his firm embankment against corrupt politicians or leaving it a bit porous.  Initially, when Anna Hazaree's hungerstrike started shaking up the slumbering Masses in India and thereafter when the moment started turning into a mass protests around the country, all the political parties seemed to have hibernate somewhere and once the strike came to an end, that hibernation ended and different political parties came with with different views over Hazaree's strike. Ironically, it's astonishing rather shameful that not a single political party, be it of national level or state level, has come out openly unconditionaly to support Haza...
Read more
Image
Himachal Pradesh has emerged as the second most drug-affected state in India after Punjab, with alarming statistics revealing that nearly 9% of schoolchildren in the state use injectable drugs, Shimla MP Suresh Kashyap informed the Lok Sabha on Wednesday. Speaking during a parliamentary session, Kashyap highlighted the growing drug menace in Himachal Pradesh, particularly among the youth. He urged the central government to take urgent steps to curb the spread of narcotics in the hill state, which has become a transit hub for drug smuggling. Alarming Drug Abuse Among Youth The revelation that 9% of school-going children are using injectable drugs has sparked serious concerns among policymakers and parents. According to Kashyap, drug abuse is rampant in districts like Kangra, Kullu, Mandi, and Shimla, where authorities have reported a sharp rise in narcotics-related cases. “Himachal Pradesh is facing a severe drug crisis, second only to Punjab. What is even more disturbing is that ...
Read more

Invest in Yourself: The Best Investment You Can Make

 If you’re looking for the smartest investment with guaranteed returns, forget about stocks, real estate, or crypto—because the best investment you can ever make is in yourself. Unlike material possessions that fade over time, the skills you learn, the habits you build, and the mindset you develop will stay with you forever. Think about it: every successful person, from entrepreneurs to top athletes, has one thing in common—they prioritize self-growth. They understand that before you can build wealth, achieve goals, or inspire others, you need to become the best version of yourself. Why Investing in Yourself Pays Off 1. You Become More Valuable In today’s fast-changing world, knowledge and skills are your biggest assets. Whether you’re upgrading your expertise, learning new technologies, or developing soft skills like communication and leadership, every step you take makes you more valuable in your career and personal life. 2. Health is the Foundation of Success You can have ...
Read more