Maharashtra Board Class 7 Science Chapter 18 Sound Production of Sound Solutions

1. Fill In The Blanks:

Question a. Sound is generated by the rhythmic ................ of any object.
Answer: vibrations
In simple words: Sound is created when an object moves back and forth rhythmically.

🎯 Exam Tip: Focus on key scientific terms like "vibrations" for fill-in-the-blanks.

Question b. The frequency of sound is measured in ................
Answer: Hertz (Hz)
In simple words: The unit that tells us how often a sound wave repeats in one second is Hertz.

🎯 Exam Tip: Remember standard units for physical quantities as they are often tested.

Question c. If ................ of sound is decreased its loudness also decreases.
Answer: intensity
In simple words: If a sound's power (intensity) goes down, it will sound quieter.

🎯 Exam Tip: Understand the direct relationship between intensity and loudness.

Question d. A medium is necessary for ................ of sound.
Answer: generation
In simple words: For sound to be made and heard, it needs something to travel through.

🎯 Exam Tip: Recall that sound is a mechanical wave and requires a medium to propagate.

2. Match The Pairs.

Question a.

Answer:

In simple words: Matching questions connect terms with their correct definitions or related concepts to test understanding of vocabulary and principles.

🎯 Exam Tip: For matching, read both columns entirely first, then identify obvious pairs, and finally tackle the trickier ones by elimination.

3. Give Scientific Reasons.

Question a. In earlier times, people used to listen for the arrival of a distant train by putting their ear to the rails.
Answer:
(i) It was a technique that worked better in those days when train speed were slower than they are today and when there were more rail joints.
(ii) When people would put their ear to the rail they could hear vibration caused by the wheels moving over the joints.
(iii) Metal being a solid is an efficient medium for the sound to travel and so the sound can propagate further in the rail than would in air as speed of sound is faster in solids than in air.
In simple words: People listened to train tracks because sound travels much faster and further through solid metal than through the air.

🎯 Exam Tip: When answering scientific reasons, always explain the underlying physical principle (e.g., speed of sound in different media).

Question b. The sounds generated by a tabla and sitar are different.
Answer:
(i) In tabla where leather is fitted, sound gets generated when the leather surface is thumped by fingers or palm.
(ii) The waves thus created travel in two dimensions. Sitar is having strings attached to pumkin box called sound box.
(iii) Sounds generated by tabla and a sitar are different because they have different pitch and frequencies.
In simple words: Tabla and sitar make different sounds because they vibrate differently-tabla uses a drumhead, sitar uses strings-leading to different pitches and frequencies.

🎯 Exam Tip: Explain how different vibrating parts (drumhead vs. strings) produce distinct sound characteristics like pitch and frequency.

Question c. If you were both on the moon your friend will not be able to hear you call.
Answer: Yes, your friend will not be able to hear your call because sound needs a medium for transmission since it is a mechanical wave it cannot travel through vaccum.
(i) As there is no air on the moon and sound is actually vibration in air.
(ii) So astronauts communicate to each other by signals or microphones in space even when they are closer.
In simple words: You can't hear on the moon because sound waves need air or another medium to travel, and there's no air in space.

🎯 Exam Tip: Emphasize that sound is a mechanical wave and its reliance on a medium for propagation.

Question d. We can hear the movement of a mosquito wings but we cannot hear the movement of our hands.
Answer:
(i) Humans cannot hear frequency less than 20 Hz. In the movement of hands oscillations does take place but is less than frequency that humans can hear.
(ii) Mosquitos wings flap in air.
(iii) When they fly in air it produces buzzing sound in our ears.
(iv) The movement of mosquito wings produces sound greater than 20 Hz.
(v) Sound is the reception of such waves and their perception by the brain.
In simple words: We hear mosquito wings because they vibrate fast enough to produce sounds within our hearing range (above 20 Hz), unlike our slow hand movements.

🎯 Exam Tip: Connect the concept of audible frequency range (20 Hz to 20,000 Hz) to explain why certain vibrations are heard and others are not.

4. Write Answers To The Following Questions.

Question a. How is sound produced?
Answer:
(i) Sound is generated due to the vibration of an object, e.g. bell, string or diaphragm of a musical instrument.
(ii) Vibrations are imparted to the molecules in the air. These vibrations reach our ears through the air and sound is heard.
(iii) Vibrations of an object is necessary for generation of sound.
(iv) These vibrations in air are called travelling longitudinal waves which we can hear.
In simple words: Sound is made when objects vibrate, pushing air molecules to create waves that travel to our ears.

🎯 Exam Tip: Clearly state that vibrations are the fundamental cause of sound production.

Question b. What does the intensity of sound depend upon?
Answer:
(i) The intensity of sound is proportional to the square of the amplitude of vibration, e.g. If the amplitude is doubled the intensity of sound becomes four times.
(ii) Therefore the loudness or softness of sound is dependent on the intensity of sound and sound level.
In simple words: The intensity of sound, which affects how loud it is, depends on the amplitude (how big the vibration is) of the sound wave.

🎯 Exam Tip: Emphasize the relationship between intensity, amplitude (specifically its square), and perceived loudness.

Question c. Explain how the frequency of oscillation is related to the length of a pendulum and the amplitude of its oscillation.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक साधारण लोलक की दोलन गति और उसके आयाम को दर्शाता है। इसमें एक धागे (Thread) से बंधी गेंद (Ball) अपने मूल स्थिति A से चरम स्थिति B और C तक झूलती हुई दिखाई गई है। A से B या A से C तक की अधिकतम दूरी को आयाम (Amplitude) कहा जाता है, जहाँ O लोलक का धुरी बिंदु है।
(i) Given an oscillatory motion to the pendulum, the maximum distance between the original position A of the pendulum and extreme position B or C is called the amplitude of oscillation. AB, AC is the amplitude of oscillation.
(ii) The number of oscillations completed by an oscillator in one second is called the frequency of oscillation.
Relation between frequency and length of a pendulum: If the length of the pendulum increases the period of oscillations also increases.
We know time period of oscillations = \( \frac{1}{\text{Frequency}} \)
\( \implies \) If time period increases, frequency decreases, therefore, if the length of the pendulum increases frequency will decrease.
Relation between frequency and amplitude: Frequency of oscillation is independent of its amplitude of oscillation.
In simple words: For a pendulum, frequency is how many swings per second. Longer pendulums swing slower (lower frequency), but the size of the swing (amplitude) doesn't change its frequency.

🎯 Exam Tip: Remember the inverse relationship between time period and frequency, and that a pendulum's frequency is primarily dependent on its length, not amplitude.

Question d. Explain the two ways by which the pitch of the sound generated by a stretched string can be changed?
Answer:
(i) A string vibrates with a particular fundamental frequency. It is however possible to produce pitches with different frequencies from the same string.
(ii) The two properties of the string that affect its frequency are length and diameter.
(iii) When the length of a string is changed, it will vibrate with a different frequency. Shorter strings have higher frequency and therefore higher pitch.
(iv) When a musician presses her finger on a string, she shortens its length. The more fingers she adds to the string, the shorter she makes it, higher will be the pitch.
Diameter: Thick strings with large diameter vibrate slower and have lower frequency than the thin ones.
In simple words: The pitch of a string's sound can be changed by altering its length (shorter means higher pitch) or its thickness/diameter (thinner means higher pitch).

🎯 Exam Tip: Focus on the physical properties of the string - length and diameter - and their direct impact on its vibration frequency and thus pitch.

Project:

Question a. The bat, a mammal, flies during the night manoeuvering with the help of the ultrasonic sounds it produces. Find out more about this.
In simple words: Bats use high-frequency sounds, called ultrasonic sounds, to navigate and find prey in the dark by listening for the echoes.

🎯 Exam Tip: Understand the concept of echolocation and how animals like bats use it for navigation and hunting.

Fill In The Blanks:

Question 1. Bats detect the obstacles in their path by receiving the reflected ................
Answer: ultrasonic waves
In simple words: Bats find their way and avoid things by listening to the echoes of their ultrasonic calls.

🎯 Exam Tip: Associate bats' navigation with ultrasonic waves and echolocation.

Question 2. An object that moves back and forth is called ................
Answer: an oscillator
In simple words: An object that repeatedly moves back and forth around a central point is known as an oscillator.

🎯 Exam Tip: Define "oscillator" correctly, linking it to objects that exhibit repetitive to-and-fro motion.

Question 3. If the length of a pendulum is increased the time period of oscillation ................
Answer: increases
In simple words: Making a pendulum longer causes it to swing slower, so its time period (time for one swing) gets longer.

🎯 Exam Tip: Recall the direct relationship between pendulum length and its time period.

Question 4. The ................ of a wave is the maximum distance moved by the object on either side of the mean position.
Answer: amplitude
In simple words: The amplitude of a wave measures the greatest distance a vibrating object moves from its resting position.

🎯 Exam Tip: Precisely define "amplitude" as the maximum displacement from the mean position.

Question 5. Sound waves do not travel through ................
Answer: vaccum
In simple words: Sound cannot travel through an empty space like a vacuum because it needs a medium to carry its vibrations.

🎯 Exam Tip: Remember that sound requires a material medium (solid, liquid, or gas) to propagate.

Question 6. The frequency above which sound is not audible to the human ear is ................
Answer: 50,000 Hz
In simple words: Humans can't hear sounds with frequencies higher than 20,000 Hz.

🎯 Exam Tip: Know the upper limit of human hearing, which is 20,000 Hz.

Question 7. Number of vibrations in a second is called ................
Answer: frequency
In simple words: The number of times an object vibrates in one second is called its frequency.

🎯 Exam Tip: Correctly define frequency as the number of oscillations per unit time.

Question 8. Higher the frequency greater will be the ................
Answer: Pitch
In simple words: A higher frequency sound will have a higher pitch, making it sound sharper.

🎯 Exam Tip: Understand the direct relationship between frequency and pitch.

Question 9. The loudness of sound depends on ................
Answer: amplitude
In simple words: How loud a sound is depends on the amplitude, or the size of its vibrations.

🎯 Exam Tip: Link the loudness of sound directly to its amplitude.

Question 10. Loudness of sound is measured in units of ................
Answer: decibel dB
In simple words: The unit used to measure the loudness of sound is the decibel, often abbreviated as dB.

🎯 Exam Tip: Know the standard unit for measuring sound loudness/intensity, which is the decibel.

Question 11. 100 hertz is equal to hundred oscillations in ................
Answer: one second
In simple words: If a sound has a frequency of 100 Hertz, it means it vibrates 100 times in just one second.

🎯 Exam Tip: Recall the definition of Hertz (Hz) as oscillations per second.

Name The Following:

Question 1. The sound frequencies above 20,000 Hz.
Answer: ultrasonic
In simple words: Sound frequencies higher than what humans can hear (above 20,000 Hz) are called ultrasonic.

🎯 Exam Tip: Distinguish between audible, infrasonic, and ultrasonic sound ranges.

Question 2. The medium through which sound is most clearly propagated.
Answer: solids
In simple words: Sound travels best and fastest through solid materials.

🎯 Exam Tip: Compare the speed of sound in solids, liquids, and gases.

Question 3. The range of frequency in which humans can hear sound.
Answer: 20-20,000 Hz
In simple words: Humans can typically hear sounds that have frequencies between 20 Hertz and 20,000 Hertz.

🎯 Exam Tip: Memorize the human audible frequency range.

Question 4. The sound level physically painful to humans.
Answer: above 100 dB
In simple words: Sound levels higher than 100 decibels are so loud they can cause pain and harm to human ears.

🎯 Exam Tip: Understand the decibel scale and identify levels that can cause harm.

Question 5. The technique used by bats to find their way.
Answer: echolocation
In simple words: Bats use a technique called echolocation, sending out sounds and listening for echoes, to navigate and locate objects.

🎯 Exam Tip: Define echolocation and provide an example of its use in nature.

Question 6. The unit of frequency of sound.
Answer: Hertz
In simple words: The standard unit for measuring the frequency of sound is Hertz (Hz).

🎯 Exam Tip: Know that Hertz (Hz) is the unit for frequency.

Question 7. The unit of sound level or intensity.
Answer: Decibel
In simple words: The unit used to quantify the intensity or level of sound is the Decibel (dB).

🎯 Exam Tip: Identify Decibel as the unit for sound level/intensity.

Question 8. The scientist in whose honour was the unit decibel named for intensity of sound.
Answer: Alexander graham Bell
In simple words: The decibel unit is named after Alexander Graham Bell, honoring his contributions to sound and communication.

🎯 Exam Tip: Connect the unit 'decibel' to the scientist Alexander Graham Bell.

Question 9. Bats and dolphins can hear these sound frequencies.
Answer: Ultra sonic sound
In simple words: Bats and dolphins are able to hear very high-frequency sounds, known as ultrasonic sound.

🎯 Exam Tip: Remember that certain animals, like bats and dolphins, have hearing ranges that extend into the ultrasonic.

Question 10. The sound frequencies used in RADAR systems.
Answer: Ultra sonic sound
In simple words: The provided answer states ultrasonic sound is used in RADAR systems for sound frequencies; however, typically RADAR uses radio waves, while SONAR uses ultrasonic sound.

🎯 Exam Tip: Differentiate between RADAR (radio waves) and SONAR (ultrasonic sound waves) for accurate understanding of their operational principles.

Answer In One Or Two Sentences:

Question 1. How is sound produced?
Answer: Sound is produced by vibration of an object.
In simple words: Sound is created when an object vibrates, causing disturbances that travel as waves.

🎯 Exam Tip: State the core principle: all sound originates from vibrations.

Question 2. What produces sound in human beings ?
Answer: The vibration of the vocal chords in our larynx or voice box produces sound.
In simple words: In humans, sound is produced by the vibrations of the vocal cords located in the voice box (larynx).

🎯 Exam Tip: Identify the vocal cords and larynx as the sound-producing structures in humans.

Question 3. What is oscillatory motion?
Answer: To and fro motion of an object (oscillator) on either side of a central position is called oscillatory motion.
In simple words: Oscillatory motion is the back-and-forth movement of an object around a fixed central point.

🎯 Exam Tip: Understand oscillatory motion as a repetitive, symmetrical movement about an equilibrium position.

Question 4. What is periodic motion?
Answer: The motion of an object repeated again and again at fixed intervals of time is called periodic motion.
In simple words: Periodic motion is any movement that repeats itself over regular, equal periods of time.

🎯 Exam Tip: Define periodic motion by highlighting its repetitive nature over fixed time intervals.

Question 5. What is frequency of oscillation?
Answer: The number of oscillations completed by an oscillator in one second is called the frequency of oscillation.
In simple words: Frequency of oscillation is how many full back-and-forth movements an object completes in one second.

🎯 Exam Tip: State the definition of frequency clearly, linking it to the number of cycles per unit time.

Question 6. How is intensity of sound and amplitude of vibration related?
Answer: The intensity of sound is proportional to the square of the amplitude of vibration. For example, if the amplitude is doubled the intensity becomes four times as much.
In simple words: The intensity of sound is directly related to the square of its amplitude; a larger vibration amplitude means much higher intensity.

🎯 Exam Tip: Remember the square relationship: intensity is proportional to (amplitude)^2.

Question 7. What happens if the frequency of sound is greater than 1000 Hz or 100 dB?
Answer: If frequency of sound is increased more than 100dB, the hearing can be temporarily affected which can result in temporary deafness.
In simple words: If sound loudness exceeds 100 dB, it can temporarily harm hearing, potentially causing temporary deafness. (The question also mentioned frequency > 1000 Hz, but the answer focused on dB).

🎯 Exam Tip: Distinguish between frequency (pitch) and intensity (loudness). High loudness (dB) is linked to hearing damage, while high frequency (Hz) might be ultrasonic but not inherently painful unless also very loud.

Question 8. What is infrasonic sound?
Answer: A sound with a frequency less than 20Hz is called infrasonic sound.
In simple words: Infrasonic sound refers to sounds with frequencies too low for humans to hear, specifically below 20 Hertz.

🎯 Exam Tip: Know the definition of infrasonic sound and its frequency range relative to human hearing.

Question 9. What is application of ultrasonic sound?
Answer: Ultrasonic sound is used in ships as a system known as 'SONAR' to detect the obstacle beneath the ocean as well as the depth of an ocean.
In simple words: Ultrasonic sound is used in SONAR systems on ships to map the ocean floor and detect objects underwater.

🎯 Exam Tip: Recall SONAR as a primary application of ultrasonic sound for underwater detection and navigation.

Question 10. What is the difference between pitch and frequency?
Answer: Pitch is directly proportional to the frequency of a sound whereas frequency is the repeating vibrations per unit time.
In simple words: Pitch is our perception of how high or low a sound is, and it's directly determined by the sound's frequency, which is the number of vibrations per second.

🎯 Exam Tip: Clearly define frequency as a physical property and pitch as the corresponding perceptual quality.

Question 11. What happens when the rubber band is stretched with a greater force and released?
Answer: When a rubber is stretched with a greater force and released, the amplitude increases which in turn result in a louder sound being generated.
In simple words: Stretching a rubber band with more force increases its vibration amplitude, leading to a louder sound when released.

🎯 Exam Tip: Understand that increasing the force of a vibration increases its amplitude, resulting in a louder sound.

Question 12. What happens to frequency if the amplitude is changed?
Answer: The frequency remains the same even if the amplitude is increased or decreased.
In simple words: Changing the amplitude of a vibration (how big the swing is) does not affect its frequency (how fast it swings).

🎯 Exam Tip: Remember that for many oscillating systems, amplitude and frequency are independent, meaning changing one doesn't necessarily change the other.

Define:

Question 1. Echo: It is a repetition of sound due to the reflection of original sound by a large and hard obstacle.
In simple words: An echo is a repeated sound you hear when sound waves bounce off a distant, hard surface.

🎯 Exam Tip: Define echo by focusing on sound reflection from a suitable barrier.

Question 2. Frequency: It is defined as the number of vibrations per unit time.
In simple words: Frequency is the measure of how many vibrations or cycles occur in a given unit of time.

🎯 Exam Tip: Provide a concise and accurate definition of frequency.

Question 3. Hertz (Hz): One hertz is one vibration per second.
In simple words: Hertz is the unit of frequency, meaning one Hertz equals one vibration per second.

🎯 Exam Tip: Clearly state the definition of Hertz and its relation to vibrations per second.

Question 4. Ultrasonic vibration: Sounds of frequency higher than 20,000 Hz are called the ultrasonic.
In simple words: Ultrasonic vibrations are sound waves that have a frequency above 20,000 Hz, which is beyond human hearing.

🎯 Exam Tip: Define ultrasonic vibrations by specifying their frequency range (above 20,000 Hz).

Question 5. Time period: The time taken by an object to complete one oscillation is called time period.
In simple words: The time period is the duration it takes for an object to complete one full back-and-forth oscillation.

🎯 Exam Tip: Clearly define time period as the time for one complete cycle of oscillation.

Question 6. Amplitude: The distance between the mean or central position to the extreme position of an oscillator on either side is called amplitude.
In simple words: Amplitude is the maximum distance an oscillating object moves from its resting or central position.

🎯 Exam Tip: Define amplitude as the maximum displacement from the equilibrium position.

Say True Or False With Explanation:

Question 1. Sound cannot travel in vacuum.
Answer: True. Sound needs a medium to travel through. Since vacuum does not provide any medium, sound cannot travel through it.
In simple words: True, sound cannot travel in a vacuum because it requires a material medium to transmit its vibrations.

🎯 Exam Tip: Reinforce that sound is a mechanical wave and requires a medium to propagate.

Question 2. If the amplitude of vibration is large, sound is feeble.
Answer: False. When the amplitude of vibration of a sound is large, the sound is very loud. The sound is feeble, when the amplitude is small. Loudness of a sound is proportional to the square of the amplitude of its vibration.
In simple words: False, a large amplitude of vibration produces a loud sound, not a feeble one, as loudness is proportional to the square of the amplitude.

🎯 Exam Tip: Correctly relate amplitude to loudness; larger amplitude means louder sound.

Question 3. For human ears, the audible range is 2 Hz to 20,000 Hz.
Answer: True. Human being can hear sounds only within the range of 20-20,000 Hz. We cannot hear the sound having frequency out of this range.
In simple words: True, the human ear can typically perceive sounds with frequencies between 20 Hz and 20,000 Hz.

🎯 Exam Tip: Accurately state the human audible frequency range.

Question 4. The lower the frequency of vibrations the higher is the pitch.
Answer: False. Pitch of sound increases when the frequency of vibration increases. The pitch of a sound is directly proportional to its frequency.
In simple words: False, lower frequency vibrations result in a *lower* pitch, as pitch is directly proportional to frequency.

🎯 Exam Tip: Clarify the direct relationship: higher frequency means higher pitch, and lower frequency means lower pitch.

Question 5. Unwanted or unpleasant sound is termed as music.
Answer: False. Unwanted, or unpleasant sounds are termed noise. Sounds which are melodious, and pleasing to ears are called music.
In simple words: False, unwanted and unpleasant sounds are called noise, while music refers to melodious and pleasing sounds.

🎯 Exam Tip: Differentiate between noise (unpleasant) and music (pleasant, rhythmic sound).

Question 6. Noise pollution may cause partial hearing impairment.
Answer: True. Unwanted, unpleasant sounds are called noise. If one is subjected to noise continuously for a long time, one may suffer from partial hearing impairment.
In simple words: True, continuous exposure to high levels of noise can indeed lead to partial hearing loss or impairment.

🎯 Exam Tip: Recognize the health risks, particularly hearing impairment, associated with prolonged exposure to noise pollution.

Question 7. Time taken by an object to complete one oscillation is called time period.
Answer: True. Time taken by an object to complete one oscillation is called time period.
In simple words: True, the duration required for an object to perform one complete oscillation is defined as its time period.

🎯 Exam Tip: Correctly define time period as the time for one complete oscillation.

Solve The Following Problems:

Question 1. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
Frequency is the number of oscillations per second of a vibrating body.
Frequency = \( \frac{\text{Number of oscillations}}{\text{Total time taken}} \)
\( = \frac{40}{4} \text{ Hz} = 10 \text{ Hz} \)
The time taken to complete one oscillation (to and fro) is known, as time period.
Time period = \( \frac{1}{\text{Frequency of oscillation}} \)
\( = \frac{1}{10} \text{ sec} = 0.1 \text{ sec} \)
In simple words: To solve this, first find frequency by dividing total oscillations by total time (40/4 = 10 Hz), then find the time period by taking the reciprocal of the frequency (1/10 = 0.1 sec).

🎯 Exam Tip: Understand the formulas for frequency and time period, and how they are inversely related.

Give Scientific Reasons

Question 1. Loud speakers should not be put in congested areas.
Answer:
1. The loudness or softness is indicated by the intensity of sound and sound level.
2. By putting loud speakers in congested areas, the intensity of sound being more than 100 dB will cause ill effects like temporary deafness and a prolonged exposure can lead to permanent damage.
In simple words: Loudspeakers in crowded areas can produce sound over 100 dB, which is harmful and can cause temporary or permanent hearing damage due to high sound intensity.

🎯 Exam Tip: Understanding the decibel (dB) scale and its relation to hearing safety is crucial for explaining the effects of noise pollution.

Answer The Following

Question 1. Why are the ceilings of concert halls curved?
Answer: The ceilings of concert halls are curved because sound after reflection from the ceiling it reaches all the comers of the hall and is audible to each person in the hall.
In simple words: Concert hall ceilings are curved to distribute sound evenly, ensuring that sound reflects to all parts of the hall, making it clearly audible to every audience member.

🎯 Exam Tip: This question tests knowledge of sound reflection and its practical applications in acoustics. Focus on the concept of uniform sound distribution.

Question 2. Have you ever heard the sound of movement of hands and falling of leaves from a tree?
Answer:
1. The term infrasonic refer to sound waves below the frequencies of audible sound i.e. under 20 Hz.
2. Humans cannot hear infrasonic sound.
3. Movement of hands and falling of leaves comes below this audible range. Therefore we cannot hear these sounds.
In simple words: Humans cannot hear the subtle sounds of hand movements or falling leaves because these sounds are typically infrasonic (below 20 Hz), which is outside the human audible frequency range.

🎯 Exam Tip: This question assesses understanding of the human hearing range and infrasonic sound. Clearly define infrasound and relate it to human auditory perception.

Question 3. How can dogs perceive in advance the signals of an impending earthquake?
Answer: Dogs can hear sounds upto about 65,000 Hz. That's why dogs can receive ultrasonic sound signals produced by the vibration of the earth and start barking in advance before the actual earthquake is felt.
In simple words: Dogs can detect early earthquake signals because their hearing range extends to ultrasonic frequencies (up to 65,000 Hz), allowing them to perceive high-frequency vibrations from the earth before humans can.

🎯 Exam Tip: Highlight the concept of ultrasonic sound and the different hearing ranges of animals compared to humans. Mentioning specific frequencies (e.g., 65,000 Hz) adds precision.

Question 4. State the uses of Ultrasonic sound.
Answer: Uses of Ultrasonic sound are:
1. To clean delicate ornaments and the tiny parts of a watch.
2. To observe internal organs of the body.
3. To detect tumors in the brain.
4. To detect faults in a metal.
5. In RADAR systems
6. To Kill certain microbes and insects.
7. SONAR (Sound navigation and ranging) is used to locate the seabed or the position of a ship.
In simple words: Ultrasonic sound has various applications, including cleaning, medical imaging (organs, tumors), detecting metal faults, RADAR, killing microbes, and SONAR for underwater navigation and mapping.

🎯 Exam Tip: List a diverse range of applications, categorizing them if possible (e.g., medical, industrial, navigation). Ensure clarity and conciseness for each use case.

Use Your Brainpower!

Answer The Following Questions:

Question 1. Will a sound be generated no matter how the ruler is kept on the table.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक मेज पर रखे गए पैमाने (रूलर) को दर्शाता है, जिसका एक हिस्सा मेज से बाहर निकला हुआ है। एक हाथ पैमाने के बाहर निकले हुए हिस्से को नीचे दबाकर छोड़ रहा है, जिससे पैमाना कंपन करता है। यह कंपन ध्वनि उत्पन्न करने की प्रक्रिया को समझाता है, जहाँ पैमाने के कंपन से वायु के अणु भी कंपन करते हैं और ध्वनि हमारे कानों तक पहुँचती है।
Answer:
1. No, If the ruler kept on the table is only a little part off the table, it will not vibrate with a greater force.
2. On the contrary if the ruler is kept with a larger portion off the table it will vibrate with a greater force generating louder sound.
In simple words: Sound generation from a vibrating ruler depends on the length extending off the table; a very small or very large free length may not produce audible sound or sufficient vibration.

🎯 Exam Tip: Focus on the relationship between the length of the vibrating object (ruler) and its amplitude/force of vibration, which determines the sound produced. Consider both frequency and loudness.

Question 2. Is there any correlation between the length of the free part of the ruler and the sound generated?
Answer: Yes, vibrating ruler pushes the molecules in the air producing sound waves. More the length of free part of ruler less will be the vibrations and less will be the frequency and pitch of the sound. If the length of free part of ruler is shorter it vibrates more quickly producing sound of higher frequency and pitch.
In simple words: Yes, there's a direct correlation: a shorter free length of the ruler results in faster vibrations, leading to higher frequency and pitch, while a longer free length leads to slower vibrations, lower frequency, and lower pitch.

🎯 Exam Tip: Emphasize the inverse relationship between the length of the vibrating object and the frequency/pitch of the sound produced. Use terms like "shorter = higher frequency/pitch" and "longer = lower frequency/pitch."

Question 3. If the ruler is plucked while it is held with 25 cm of it off the table, does it makes any sound? If there is no sound, look for the reason why it is so?
Answer: No, the ruler vibrates very slowly, which has frequency which is not audible.
In simple words: If a ruler with 25 cm extending off the table is plucked, it likely won't produce an audible sound because its vibrations would be very slow, resulting in a frequency below the human hearing range.

🎯 Exam Tip: Relate the length of the vibrating object to its frequency and the human audible range (20 Hz - 20,000 Hz). A very long free length often results in infrasonic vibrations.

Question 4. What would be the difference perceived between hearing only two pupils in the class talking to each other and all the children talking to one another at the same time?
Answer:
1. When two pupils talk to each other, the sounds of two frequencies produced can be heard clearly.
2. When all the children talk to one another sounds of many frequencies produced can not be heard clearly.
3. Sound level will be more creating loud noise.
In simple words: Hearing two pupils talking allows for clear perception of individual frequencies, whereas many children talking simultaneously creates a mix of numerous frequencies, resulting in unclear, louder sound that is perceived as noise.

🎯 Exam Tip: Differentiate between clear sound and noise based on the number of sound sources and the resulting complexity of frequencies. Discuss how multiple simultaneous sounds contribute to an increased sound level and perceived noise.