Case based Questions: Sound

Q1: Read the following passage and answer the questions that follow:

i. Why does the ball move when touched by the vibrating tuning fork? (1 mark)
ii. What does this experiment demonstrate about the nature of sound production? (2 mark)
iii. Can sound be produced without vibration? Justify your answer. (1 mark)

Ans:

i. The vibrating tuning fork transfers energy to the ball, making it move. This shows that sound waves carry energy.
ii. This experiment shows that sound is produced by vibrating objects. When the tuning fork is struck its prongs vibrate and these vibrations set the air particles around them into motion, producing the sound we hear.
iii. No, sound cannot be produced without vibration because sound is a wave generated by oscillations of matter. All familiar sound sources - vibrating strings, vocal cords, tuning forks, and speakers - produce sound by making particles of the surrounding medium vibrate.

Q2: Read the following passage and answer the questions that follow:

i. What kind of wave is a sound wave, and how does it propagate?(1 mark)
ii. How does the motion of particles in a sound wave differ from a water wave?(2 mark)
iii. Explain why sound cannot travel in a vacuum.(1 mark)

Ans:
i. Sound is a longitudinal wave. It propagates as alternating regions of compression (high pressure) and rarefaction (low pressure) through a material medium such as air.
ii. In a sound wave, individual particles of the medium move back and forth parallel to the direction the wave travels (for example, along the coils of a slinky). In a typical water wave, particles move in roughly circular or up-and-down paths, which is largely perpendicular to the direction the wave travels.
iii. Sound cannot travel in a vacuum because there are no particles to carry the vibrations. 

Q3: Read the following passage and answer the questions that follow:

i. Why are they unable to hear each other on the Moon? (1 mark)
ii. How does the absence of a medium affect sound transmission? (2 mark)
iii. What method can they use to communicate instead? (1 mark)

Ans:
i. They cannot hear each other because the Moon has no atmosphere and therefore no air to act as a medium for sound waves.
ii. Without a medium there are no particles to vibrate, so compressions and rarefactions cannot form or travel. As a result, sound waves cannot be transmitted from one person to another in a vacuum.
iii. They can use radio communication. Radio waves are electromagnetic and do not require a material medium, so they can travel through vacuum.

Q4: Read the following passage and answer the questions that follow:

i. Which property of sound is responsible for the difference in sounds produced by different strings? (1 mark)
ii. How does the length of the string affect the pitch of the sound? (2 mark)
iii. Why do musical instruments have different tones even when playing the same note? (1 mark)

Ans:
i. The property responsible is pitch, which depends on the frequency of vibration of the string.
ii. Shorter strings vibrate faster and so produce higher frequencies (higher pitch). Longer strings vibrate more slowly and produce lower frequencies (lower pitch). 
iii. Different instruments produce different sets of overtones and harmonics even for the same fundamental frequency. These extra frequencies change the sound's quality or timbre, so the same note sounds different on different instruments.

Q5: Read the following passage and answer the questions that follow:

i. Why does the flash of lightning appear before the sound of thunder? (1 mark)
ii. Which factor determines the time delay between the two events? (2 mark)
iii. If the person is closer to the storm, how will this affect the delay?(1 mark)

Ans:
i. Light from the lightning reaches the observer almost instantly because light travels much faster than sound. Sound (thunder) travels much more slowly, so it arrives later.
ii. The time delay depends mainly on the distance from the lightning to the observer and on the speed of sound in air . 
iii. If the person is closer to the storm, the delay will be shorter because the sound has a smaller distance to travel before reaching the observer.

Q6: Read the following passage and answer the questions that follow:

Ans:
i. An echo is the sound heard when a sound wave is reflected from a distant surface and returns to the listener after a short time.
ii. Calculation:
Time for the sound to travel to the building and back = 2.0 s.
Total distance travelled by sound = speed × time = 340 m/s × 2.0 s = 680 m.
Distance to the building = (total distance)/2 = 680 m / 2 = 340 m.
iii. On a hotter day the speed of sound in air is higher, so the echo would return faster. 

Q7: Read the following passage and answer the questions that follow:

i. What is the formula for calculating the wavelength of a wave? (1 mark)
ii. Calculate the wavelength of the sound wave. (2 mark)
iii. If the sound wave travels through water where the speed of sound is 1500 m/s, what will be the new wave length? (1 mark)

Ans:
i. Wavelength, λ = speed of wave / frequency, i.e. λ = v / f.
ii. λ = 340 m/s ÷ 500 Hz = 0.68 m.
iii. In water λ = 1500 m/s ÷ 500 Hz = 3.0 m.

Q8: Read the following passage and answer the questions that follow:

i. What is the relationship between speed, frequency, and wave length? (1 mark)
ii. Calculate the wavelength of the sound wave. (2 mark)
iii. If the frequency is doubled, what happens to the wave length? (1 mark)

Ans:
i. The relation is v = λ × f, where v is speed, λ is wavelength and f is frequency.
ii. λ = v / f = 340 m/s ÷ 256 Hz ≈ 1.33 m.
iii. If the frequency is doubled to 512 Hz, the wavelength is halved: λ = 340 ÷ 512 ≈ 0.664 m.

Q9: Read the following passage and answer the questions that follow:

i. Why do bats use ultrasonic waves?(1 mark)
ii. Calculate the wavelength of the emitted wave. (2 mark)
iii. If the bat is in water where the speed of sound is 1500 m/s, what would be the new wave length? (1 mark)

Ans:
i. Bats use ultrasound for echolocation because high frequencies have short wavelengths, which let bats detect small objects and precise positions of prey or obstacles.
ii. Frequency f = 40 kHz = 40 000 Hz. 
λ = v / f = 340 m/s ÷ 40 000 Hz = 0.0085 m (8.5 mm).
iii. In water λ = 1500 m/s ÷ 40 000 Hz = 0.0375 m (37.5 mm).

Q10: Read the following passage and answer the questions that follow:

i. What causes the delay between seeing and hearing the horn?(1 mark)
ii. Calculate the distance of the train.(2 mark)
iii. If the person was underwater, would the delay be shorter or longer? (1 mark)

Ans:
i. Light reaches the observer much faster than sound, so the train is seen almost instantly while the sound takes time to travel to the observer, causing the delay.
ii. Distance = speed × time = 343 m/s × 1.5 s = 514.5 m.
iii. Shorter. Sound travels faster in water (about 1500 m/s) than in air, so the same sound would reach the observer sooner underwater.

Q11: Read the following passage and answer the questions that follow:

i. What is the phenomenon responsible for the sound continuing in the empty room? (1 Mark)
ii. How do curtains and carpets affect the sound in the second case? (2 Mark)
iii. Why is a concert hall designed with materials that absorb sound? (1 Mark)

Ans:
i. The phenomenon is reverberation - multiple reflections of sound from hard surfaces make the sound persist for some time after the source stops.
ii. Curtains and carpets absorb a large part of the sound energy instead of reflecting it. This absorption reduces the number and strength of reflections, so the sound dies away quickly and the room sounds less echoey.
iii. Concert halls use sound-absorbing and diffusing materials to control reverberation so that music and speech remain clear and not muddled. Proper design gives good clarity, balance and pleasant acoustics for the audience.

Q12: Read the following passage and answer the questions that follow:

A ship in the ocean sends ultrasonic waves toward the sea floor to measure its depth. The waves reflect back after hitting the ocean bed, and the time taken for the echo to return is recorded.

i. What is the name of this technique used for measuring depth?(1 mark)
ii. Why are ultrasonic waves used instead of normal sound waves?(2 mark)
iii. How does increasing the speed of sound in water affect the measurement?(1 mark)

Ans:
i. This technique is called SONAR (Sound Navigation And Ranging).
ii. Ultrasonic waves are used because their high frequency and short wavelength give better resolution and allow precise detection of the sea bed and objects. They also travel well through water for the required distances.
iii. If the speed of sound in water increases, the depth measurement will change because the time taken for the echo to return will be shorter.

Q13: Read the following passage and answer the questions that follow:

i. Which property of sound is responsible for this difference?(1 mark)
ii. What factors determine the quality of sound produced by an instrument? (2 mark)
iii. How does the waveform of sound affect the perception of different instruments? (1 mark)

Ans:
i. The property is timbre (also called quality of sound).
ii. Timbre depends on the waveform and on the presence and relative strengths of overtones and harmonics. The material, shape and construction of the instrument, and the way it is played, also affect which overtones are produced and so change the quality.
iii. The waveform shows how the pressure varies with time and thus contains the mix of frequencies present. Different instruments produce different waveforms with different harmonic content, so the ear recognises each instrument by these differences in waveform and overtone structure.

Q14: Read the following passage and answer the questions that follow:

i. Why does the sound become fainter as air is removed from the chamber? (1 mark)
ii. What does this experiment demonstrate about the propagation of sound? (2 mark)
iii. If the mobile phone were placed inside a water tank instead of a vacuum chamber, would the sound still be heard? Why? (1 mark)

Ans:
i. As the air is removed there are fewer particles to carry the vibrations from the phone to the listener, so the sound becomes fainter and finally cannot travel at all in the near vacuum.
ii. The experiment demonstrates that sound needs a material medium (solid, liquid or gas) to travel; it cannot propagate through a vacuum where there are no particles to transmit the vibrations.
iii. Yes, sound can travel in water because water has particles that carry sound vibrations, although it may sound different.

Q15: Read the following passage and answer the questions that follow:

i. Why is the sound of the train heard earlier through the railway track than through the air? (1 mark)
ii. How does the speed of sound vary in solids, liquids, and gases? (2 mark)
iii. Why do earthquake waves travel faster through the Earth's crust than through the air? (1 mark)

Ans:
i. Sound travels faster in solids like the steel rail than in air, so vibrations from the train reach the ear on the track sooner than the sound waves travelling through the air.
ii. In general sound travels fastest in solids, slower in liquids, and slowest in gases. This is because particles in solids are more closely packed and interact more strongly, allowing vibrations to pass more quickly.
iii. Earthquake (seismic) waves travel faster through the Earth's crust because rock is a solid with tightly packed particles, which transmits mechanical vibrations much more quickly than air. This is why seismic detectors can register waves over long distances.