Characteristics of Sound – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Explain how sound travels as longitudinal waves. Use the slinky activity to support your explanation.
Answer:
- Sound travels as longitudinal waves.
- The particles of the medium move back and forth in the same direction as the wave.
- These back-and-forth regions form compressions and rarefactions.
- In compressions, particles are close together. In rarefactions, particles are far apart.
- A slinky shows this well. Push and pull the slinky to see compressions and rarefactions move.
- This is how your voice travels through air to reach others.
- So, sound needs a medium and travels by passing on vibrations.
Q2. Describe how amplitude affects the loudness of sound with daily life examples.
Answer:
- Amplitude is the maximum displacement of particles from rest.
- A larger amplitude means a louder sound.
- A smaller amplitude means a softer sound.
- A loud drum beat has high amplitude. A soft whisper has low amplitude.
- Amplitude is linked to the energy of the sound wave. More energy, more amplitude.
- Loud sounds can feel strong because they push air particles more.
- So, amplitude mainly controls loudness, not pitch.
Q3. What is frequency? How does it relate to pitch? Explain with examples.
Answer:
- Frequency is the number of waves passing a point in one second.
- Its unit is Hertz (Hz).
- A higher frequency gives a higher pitch.
- A lower frequency gives a lower pitch.
- A whistle has high frequency and sounds shrill.
- A bass drum has low frequency and sounds deep.
- So, pitch depends mainly on frequency of vibration.
Q4. Explain wavelength. How is it connected to frequency and pitch?
Answer:
- Wavelength is the distance between two points in the same phase.
- For example, from one compression to the next compression.
- If frequency increases, wavelength decreases in the same medium.
- If frequency decreases, wavelength increases in the same medium.
- Higher pitch sounds (like C#) have shorter wavelengths.
- Lower pitch sounds (like note A) have longer wavelengths.
- In a given medium, speed stays the same, so frequency and wavelength adjust together.
Q5. Why does sound travel fastest in solids, slower in liquids, and slowest in gases? Give examples.
Answer:
- In solids, particles are close together. Vibrations pass quickly.
- In liquids, particles are less close than solids. Speed is moderate.
- In gases, particles are far apart. Vibrations take longer to pass.
- So, sound is fastest in solids, slower in liquids, slowest in gases.
- Example speeds: steel ≈ 5000 m/s, water ≈ 1500 m/s, air ≈ 343 m/s.
- Thus, you can hear taps through metal faster than through air.
- The closeness of particles controls the speed of sound.
High Complexity (Analysis & Scenario-Based)
Q6. You strike a classroom wall and also shout at the same time. A friend on the other side listens with an ear on the wall and also through the air. Which sound reaches first and why?
Answer:
- The sound through the wall (solid) reaches first.
- Sound travels fastest in solids because particles are close.
- The wall carries vibrations quickly from your strike.
- The shout travels through air (gas), which is slower.
- Air particles are far apart, so vibration transfer is slower.
- So, the friend hears the tap earlier via the wall than the shout through air.
- This shows how medium changes the speed of sound.
Q7. You try to measure the speed of sound outdoors using a clap and echo. Explain the steps, sources of error, and ways to improve accuracy.
Answer:
- Stand far from a large wall and clap once.
- Use a stopwatch to time the echo return.
- Measure or estimate the distance to the wall. The sound travels to and fro.
- Compute speed as: total distance divided by time taken.
- Errors: reaction time in starting/stopping, wind, background noise, distance estimate.
- Improve by taking many readings and averaging.
- Use a phone recorder to see time more clearly and reduce human error.
Q8. In a drum, how does tightening the drum skin change the sound? Discuss in terms of frequency, amplitude, and pitch.
Answer:
- Tightening the skin makes it vibrate faster.
- Faster vibration means higher frequency.
- Higher frequency gives a higher pitch sound.
- The sound may also become sharper and more clear.
- If you hit harder, amplitude increases, so sound is louder.
- If you hit softly, amplitude is low, so it is softer.
- Thus, tension mainly changes frequency and pitch, while force changes amplitude and loudness.
Q9. You try to talk to a friend underwater at a short distance. Why does speech sound unclear even though sound is faster in water?
Answer:
- Sound travels faster in water than in air.
- But our ears are designed to receive sound best through air.
- Underwater, sound reaches us through different pathways, so speech feels muffled.
- The wavelength in water is longer for the same frequency, changing how we perceive it.
- Also, forming clear sounds needs air in our mouth and nose. Underwater, that is missing.
- So, even with higher speed, speech sounds unclear to us in water.
- The medium affects both travel and perception.
Q10. A tuning fork sounds normal in air. When you press its handle on a metal table, it sounds louder. Explain why using ideas of medium and vibration transfer.
Answer:
- The tuning fork vibrates and makes nearby air vibrate.
- Air is a gas, so it passes vibrations slowly and with less energy.
- A metal table is a solid, so it passes vibrations faster and more efficiently.
- The table also has a large surface area. It pushes more air and makes louder sound.
- More air set into motion means greater amplitude and loudness.
- Thus, contact with solid metal boosts transmission and sound output.
- This is why the sound becomes louder and clearer on the table.