Q1: How is sound produced?

Answer: Sound is produced by vibrations. When an object vibrates, it sets the particles of the surrounding medium (like air, water, or solids) into oscillatory motion, creating a disturbance that travels as a sound wave.

Q2: Why does sound need a medium to travel?

Answer: Sound is a mechanical wave, meaning it requires a material medium (solids, liquids, or gases) for its propagation. It travels by causing the particles of the medium to vibrate and transfer energy from one particle to the next. In a vacuum, there are no particles to vibrate, so sound cannot travel through it.

Q3: What type of wave is a sound wave? Explain briefly.

Answer: A sound wave is a **longitudinal wave**. In a longitudinal wave, the particles of the medium vibrate parallel to the direction of wave propagation. As sound travels, it creates regions of high pressure (compressions) and low pressure (rarefactions) in the medium.

Q4: In which medium does sound travel fastest: solid, liquid, or gas? Why?

Answer: Sound travels fastest in **solids**, slower in liquids, and slowest in gases. This is because particles in solids are more closely packed and rigidly arranged than in liquids or gases, allowing vibrations (and thus sound energy) to be transmitted more efficiently and quickly from one particle to the next.

Q5: Define wavelength ($\lambda$) and frequency ($\nu$) of a sound wave.

Answer:

• Wavelength ($\lambda$): It is the distance between two consecutive compressions or two consecutive rarefactions (or any two consecutive identical points) of a sound wave. Unit: meter (m).
• Frequency ($\nu$): It is the number of complete oscillations or vibrations of a particle of the medium per unit time. It determines the pitch of the sound. Unit: Hertz (Hz).

Q6: How are the speed, frequency, and wavelength of a sound wave related?

Answer: The speed ($v$), frequency ($\nu$), and wavelength ($\lambda$) of a sound wave are related by the formula:
$v = \nu \lambda$
(Speed = Frequency × Wavelength)

Q7: What determines the pitch of a sound? Give an example.

Answer: The pitch of a sound is determined by its **frequency**. A higher frequency results in a higher pitch (shrill sound), while a lower frequency results in a lower pitch (flat sound). Example: A child's voice typically has a higher pitch (higher frequency) than an adult male's voice.

Q8: What determines the loudness of a sound? What is its unit?

Answer: The loudness of a sound is determined by its **amplitude**. A larger amplitude corresponds to a louder sound, and a smaller amplitude corresponds to a softer sound. The unit of loudness is the **decibel (dB)**.

Q9: What is the quality (timbre) of a sound? How does it help us?

Answer: The quality or timbre of a sound is that characteristic which enables us to distinguish between two sounds of the same pitch and loudness produced by different sources. It depends on the mixture of different frequencies (overtones) present in the sound wave. Example: We can distinguish between the sound of a piano and a flute playing the same note due to their different qualities.

Q10: What is an echo? What is the minimum distance required to hear a distinct echo in air at 22°C?

Answer: An echo is the repetition of sound caused by the reflection of sound waves from a distant hard surface or obstacle. To hear a distinct echo in air at 22°C, the minimum distance between the source of sound and the reflecting surface should be approximately **17.2 meters**.

Q11: Explain the phenomenon of reverberation. How can it be reduced?

Answer: Reverberation is the persistence of sound in a large hall or auditorium due to repeated reflections from the walls, ceiling, and floor, even after the sound source has stopped. Excessive reverberation can make speech unclear. It can be reduced by using sound-absorbing materials (e.g., curtains, carpets, acoustic panels, false ceilings) on the surfaces of the hall.

Q12: What is the audible range of frequency for the average human ear?

Answer: The audible range of frequency for the average human ear is approximately **20 Hz to 20,000 Hz (20 kHz)**.

Q13: Differentiate between infrasound and ultrasound. Give one example of an animal that uses each.

Answer:

• Infrasound: Sounds with frequencies below 20 Hz. Inaudible to humans. Example: Elephants communicate using infrasound.
• Ultrasound: Sounds with frequencies above 20,000 Hz (20 kHz). Inaudible to humans. Example: Bats use ultrasound for echolocation (finding prey and navigating).

Q14: List three medical applications of ultrasound.

Answer: Three medical applications of ultrasound are:

1. Ultrasound Imaging (Sonography): To image internal organs (e.g., fetus during pregnancy, heart, liver).
2. Breaking Kidney Stones: High-intensity ultrasound waves can break kidney stones into smaller pieces.
3. Echocardiography: Used to obtain images of the heart.

Q15: Explain the principle of SONAR. What is its full form?

Answer: SONAR stands for **Sound Navigation And Ranging**. Its principle is based on the reflection of ultrasonic waves. A sonar device sends ultrasonic waves into the water. These waves travel, hit an object (like a submarine, shipwreck, or fish school), and are reflected back as an echo to the detector. By measuring the time taken for the echo to return and knowing the speed of sound in water, the distance to the object can be calculated.

Q16: Describe the function of the outer ear in humans.

Answer: The outer ear consists of the pinna (the visible part) and the ear canal (auditory canal). Its primary function is to collect sound waves from the surroundings and direct them through the ear canal to the eardrum (tympanic membrane).

Q17: What are the three tiny bones in the middle ear called? What is their function?

Answer: The three tiny bones in the middle ear are called **ossicles**: Malleus (hammer), Incus (anvil), and Stapes (stirrup). Their function is to amplify and transmit the vibrations from the eardrum to the inner ear, efficiently transferring sound energy.

Q18: Which part of the human ear converts sound vibrations into electrical signals?

Answer: The **cochlea** in the inner ear is responsible for converting the mechanical vibrations received from the middle ear into electrical signals. These electrical signals are then sent to the brain via the auditory nerve for interpretation as sound.

Q19: A sound wave has a frequency of 500 Hz and a wavelength of 0.6 m. Calculate its speed.

Answer: Given: Frequency ($\nu$) = 500 Hz, Wavelength ($\lambda$) = 0.6 m
Using formula: $v = \nu \lambda$
$v = 500 \text{ Hz} \times 0.6 \text{ m}$
$v = 300 \text{ m/s}$
Speed of sound = 300 m/s.

Q20: Why do empty halls often have more reverberation than furnished rooms?

Answer: Empty halls have more reverberation because their hard, bare surfaces (walls, ceiling, floor) are good reflectors of sound. Sound waves repeatedly reflect off these surfaces, causing the sound to persist for a longer time. Furnished rooms, on the other hand, have carpets, curtains, furniture, and other soft materials that absorb sound waves, reducing reflections and thus minimizing reverberation.

Q21: How do bats use ultrasound for hunting?

Answer: Bats use a technique called echolocation. They emit high-frequency ultrasonic waves. These waves travel outwards, hit obstacles or prey (like insects), and reflect back as echoes. Bats listen to these echoes, and by analyzing the time taken for the echo to return, its direction, and intensity, they can accurately determine the location, size, and movement of objects in their environment, even in complete darkness.

Q22: What is the purpose of the Eustachian tube in the human ear?

Answer: The Eustachian tube connects the middle ear to the back of the throat. Its primary purpose is to equalize the air pressure on both sides of the eardrum (tympanic membrane). This equalization is crucial for the eardrum to vibrate freely and for clear hearing. When there's a sudden change in external pressure (e.g., during flight or diving), the Eustachian tube opens to balance the pressure.

Q23: Can sound travel through the vacuum of space? Explain why or why not.

Answer: No, sound cannot travel through the vacuum of space. Sound is a mechanical wave that requires a medium (like air, water, or solid material) to propagate. In the vacuum of space, there are virtually no particles to vibrate and transmit sound energy, so sound waves cannot travel from one point to another.

Q24: A person shouts near a cliff and hears an echo after 4 seconds. If the speed of sound in air is 340 m/s, how far away is the cliff?

Answer: Given: Time taken for echo ($t$) = 4 s Speed of sound ($v$) = 340 m/s
The sound travels to the cliff and back, so the total distance covered is $2d$.
Total distance = Speed × Time
$2d = v \times t$
$2d = 340 \text{ m/s} \times 4 \text{ s}$
$2d = 1360 \text{ m}$
Distance to the cliff ($d$) = $1360 / 2 = 680 \text{ m}$
The cliff is 680 meters away.

Q25: Why do musical instruments sound different even when playing the same note at the same loudness?

Answer: Musical instruments sound different even when playing the same note (same pitch/frequency) at the same loudness (same amplitude) due to their unique **quality or timbre**. The quality of sound depends on the complex mixture of fundamental frequency and overtones (harmonics) produced by each instrument. This unique waveform gives each instrument its characteristic sound, allowing us to distinguish a guitar from a violin, even if they play the same note.