Sound — Previous Year Questions (Class 8 Science)
Understand sound as a wave, vibrations, and how sound travels through different media. Learn frequency, pitch, and loudness.
TL;DR: Understand sound as a wave, vibrations, and how sound travels through different media. Learn frequency, pitch, and loudness.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Understand sound as a wave, vibrations, and how sound travels through different media. Learn frequency, pitch, and loudness.
Sound — Previous Year Questions with Solutions
Q (2023, 3 marks): What is sound? How is sound produced?
Answer: Sound: A form of energy produced by vibrations that travels in the form of waves.
How sound is produced: When an object vibrates, it causes the particles in the surrounding medium (air, water, etc.) to vibrate. These vibrations create sound waves that travel outward.
Example: When a tuning fork is struck, it vibrates and produces sound.
Q (2022, 2 marks): Differentiate between frequency and pitch.
Answer: Frequency: The number of vibrations per second. Measured in Hz (Hertz). It is a physical property.
Pitch: How high or low a sound seems to our ear. It depends on frequency. Higher frequency = higher pitch; lower frequency = lower pitch.
Frequency is measurable; pitch is perceptual.
Q (2023, 2 marks): Can sound travel through a vacuum? Explain.
Answer: No, sound cannot travel through a vacuum.
Reason: Sound requires a medium (solid, liquid, or gas) to propagate. In a vacuum, there are no particles to vibrate and carry the sound waves.
Sound speed varies: Sound travels fastest in solids, slower in liquids, and slowest in gases.
Q (2022, 3 marks): What is echo? Under what conditions does an echo occur?
Answer: Echo: A repetition of sound caused by reflection of sound waves from a surface.
Conditions for echo:
1. Source of sound
2. A reflecting surface (wall, cliff, etc.)
3. The reflecting surface must be at least 17 meters away
4. The reflected sound must reach the ear after the original sound ends
Example: Clapping in a valley produces an echo due to sound reflection from the hills.
Q (2023, 2 marks): A sound wave has a frequency of 500 Hz. Calculate the period of vibration.
Answer: Frequency = 500 Hz
Period = 1 / Frequency
Period = 1 / 500 = 0.002 seconds = 2 milliseconds
Q (2022, 3 marks): Why do we sometimes hear thunder after seeing lightning?
Answer: Light travels much faster than sound.
Speed of light: 3 × 10^8 m/s (almost instantaneous)
Speed of sound: 340 m/s (much slower)
So we see lightning immediately but hear the thunder after a delay. The delay depends on the distance: Distance = Speed × Time delay
This is why we see lightning first and hear thunder later.
Frequently Asked Questions
What is the audible range of human hearing?
The human ear can hear sounds with frequencies roughly between 20 Hz and 20,000 Hz (20 kHz). Sounds below 20 Hz are called infrasound (though we feel them as vibrations). Sounds above 20 kHz are called ultrasound.
What is loudness and what factors affect it?
Loudness is the intensity of sound as perceived by the human ear. It is measured in decibels (dB). Factors affecting loudness include: (1) The amplitude of sound waves (larger amplitude = louder), (2) The distance from the source (closer = louder), (3) The medium through which sound travels.
More Class 8 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
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