How to Use This Page
Read each question carefully and try to answer it on your own before checking the solution. Use the Key Concepts table for a quick review of definitions, then work through the MCQs, fill-in-the-blanks, and true/false sections for practice. The Common Mistakes and Exam Checklist at the end will help you avoid frequent errors and ensure you are fully prepared for your exam.
Key Concepts (Quick Recap)
| Term | Definition |
|---|---|
| Sound production | Sound is produced when an object vibrates, creating compressions and rarefactions in the surrounding medium |
| Vibration | A rapid to-and-fro motion of an object about its mean (rest) position |
| Frequency | The number of vibrations or oscillations per second, measured in Hertz (Hz) |
| Amplitude | The maximum displacement of a vibrating body from its rest position; determines loudness |
| Time period | The time taken for one complete vibration or oscillation, measured in seconds (s) |
| Wavelength | The distance between two consecutive compressions (or rarefactions) in a sound wave |
| Pitch | How high or low a sound is perceived; depends on frequency — higher frequency means higher pitch |
| Loudness | The perceived intensity of sound; depends on amplitude — greater amplitude means louder sound |
| Medium | A material (solid, liquid, or gas) through which sound travels; sound cannot travel in a vacuum |
| Longitudinal wave | A wave in which particles of the medium vibrate parallel to the direction of wave propagation |
| Echo | A reflected sound that is heard after a short delay; requires a minimum distance of ~17 m from the reflecting surface |
| Ultrasonic sound | Sound with frequency above 20,000 Hz; inaudible to humans but used in medical imaging and cleaning |
| Infrasonic sound | Sound with frequency below 20 Hz; inaudible to humans; produced by earthquakes and detected by some animals |
I. Choose the Best Answer (MCQs)
Q1. Sound waves cannot travel through
- (a) Air (b) Water (c) Vacuum (d) Steel
Q2. The unit of frequency is
- (a) Hertz (b) Decibel (c) Pascal (d) Newton
Q3. Which of the following determines the pitch of a sound?
- (a) Amplitude (b) Frequency (c) Wavelength (d) Time period
Q4. The loudness of sound is determined by its
- (a) Frequency (b) Amplitude (c) Wavelength (d) Velocity
Q5. In which medium does sound travel the fastest?
- (a) Air (b) Water (c) Vacuum (d) Iron
Q6. The maximum displacement of a vibrating body from its rest position is called
- (a) Frequency (b) Amplitude (c) Time period (d) Wavelength
Q7. Which of the following is an example of a stringed instrument?
- (a) Flute (b) Table (c) Veena (d) Mridangam
Q8. The time period of a sound wave is 0.02 s. Its frequency is
- (a) 20 Hz (b) 50 Hz (c) 100 Hz (d) 500 Hz
Q9. An echo is heard when sound is reflected from a surface. The minimum distance required to hear a distinct echo is approximately
- (a) 10 m (b) 17 m (c) 34 m (d) 100 m
Q10. The speed of sound in air at room temperature (about 20°C) is approximately
- (a) 220 m/s (b) 330 m/s (c) 340 m/s (d) 512 m/s
Q11. Which of the following instruments produces sound by vibrating a stretched membrane?
- (a) Violin (b) Shehnai (c) Mridangam (d) Guitar
II. Fill in the Blanks
1. Sound is produced by vibrations of objects. 2. Sound travels the fastest in solids among the three states of matter. 3. The number of vibrations per second is called frequency. 4. The SI unit of frequency is Hertz (Hz). 5. The maximum displacement of a vibrating body from its rest position is called amplitude. 6. The time taken for one complete vibration is called the time period. 7. Sound cannot travel through vacuum. 8. Loudness of sound is measured in decibels (dB). 9. The human ear can hear sounds in the frequency range of 20 Hz to 20,000 Hz. 10. Sound needs a medium to travel. 11. The repetition of sound caused by reflection from a hard surface is called an echo. 12. The distance between two consecutive compressions (or rarefactions) in a sound wave is called the wavelength.
III. True or False
IV. Match the Following
| Column I | Column II | Answer |
|---|---|---|
| Frequency | Hertz | Frequency — Hertz |
| Amplitude | Loudness | Amplitude — Loudness |
| Time period | Second | Time period — Second |
| Pitch | Shrillness | Pitch — Shrillness |
| Decibel | Intensity of sound | Decibel — Intensity of sound |
V. Short Answer Questions
Q1. How is sound produced? Answer: Sound is produced when an object vibrates. The vibrating object creates disturbances in the surrounding medium (air, water, or solid), which travel as longitudinal waves and reach our ears as sound. For example, plucking a guitar string makes it vibrate and produce sound. Without vibration, there is no sound — even when we speak, our vocal cords inside the throat vibrate to create the sound of our voice.
Q2. Why does sound need a medium to travel? Answer: Sound travels as a mechanical wave by transferring energy from one particle to the next through vibrations. In a vacuum, there are no particles to vibrate and transfer the disturbance, so sound cannot propagate. This is why astronauts on the Moon cannot hear each other directly and must use radio communication — the Moon has no atmosphere to carry sound waves.
Q3. What is the difference between musical sound and noise? Answer:
- Musical sound: Pleasant to hear, has a regular waveform, definite frequency, and fixed pattern (e.g., flute, veena). Musical sounds are produced by periodic vibrations that repeat at regular intervals.
- Noise: Unpleasant to hear, has an irregular waveform, no definite frequency or pattern (e.g., traffic sounds, construction noise). Noise results from non-periodic, random vibrations that lack a consistent pattern.
Q4. What is the time period of a sound wave? How is it related to frequency? Answer: The time period (T) is the time taken for one complete vibration or oscillation. It is related to frequency (f) by the formula: T = 1/f, or f = 1/T. The SI unit of time period is seconds. For example, if a tuning fork vibrates 100 times per second (f = 100 Hz), its time period is T = 1/100 = 0.01 seconds. Frequency and time period are inversely proportional — as one increases, the other decreases.
Q5. Name the three types of musical instruments and give one example for each. Answer: 1. Stringed instruments: Produce sound by vibrating strings. Example: Veena, Guitar. The pitch can be changed by varying the tension, thickness, or length of the string. 2. Wind instruments: Produce sound by vibrating air columns. Example: Flute, Nadaswaram. The pitch changes with the length of the air column. 3. Percussion instruments: Produce sound by vibrating stretched membranes. Example: Table, Mridangam. Striking the membrane at different points produces different tones.
Q6. Why do we see lightning before we hear thunder? Answer: Light travels at approximately 3 × 10^8 m/s, while sound travels at about 330 m/s in air. Light is much faster than sound, so we see the lightning first and hear the thunder later. The time gap between seeing lightning and hearing thunder can be used to estimate the distance of the storm — roughly every 3-second delay equals about 1 km of distance.
Q7. What is ultrasonic sound? Give two uses. Answer: Ultrasonic sounds have frequencies above 20,000 Hz and cannot be heard by humans. Uses: 1. Ultrasonography (medical imaging to view internal organs and monitor fetal development during pregnancy). 2. Cleaning delicate instruments and removing dust from tiny crevices where brushes cannot reach. 3. Detecting flaws in metal structures and welding joints in industrial applications.
Q8. What is infrasonic sound? Give one example. Answer: Infrasonic sounds have frequencies below 20 Hz and cannot be heard by humans. Example: Earthquakes produce infrasonic waves before the main shock; some animals like elephants and whales can detect infrasonic sounds and use them for long-distance communication. Infrasonic waves can travel over very long distances because they lose less energy than higher-frequency waves.
Q9. What is an echo? Under what conditions can a distinct echo be heard? Answer: An echo is the repetition of sound caused by the reflection of sound waves from a hard surface such as a cliff, wall, or building. For a distinct echo to be heard, the reflecting surface must be at least 17 m away from the listener. This ensures that the reflected sound reaches the ear at least 0.1 seconds after the original sound, allowing the human ear to distinguish the echo from the original sound.
VI. Detailed Answer Questions
Q1. Explain the production and propagation of sound with an example. Answer: Production: Sound is produced by vibrating objects. When an object vibrates, it pushes and pulls the air around it, creating alternating regions of compression (high pressure) and rarefaction (low pressure). These pressure variations are the essence of a sound wave.
Propagation: These compressions and rarefactions travel outward from the source as longitudinal waves. The particles of the medium simply oscillate about their mean position; they do not travel with the wave. The energy transfers from one particle to the next in a chain reaction, much like a domino effect. The medium itself is not transported — only the disturbance moves forward.
Example: When a tuning fork is struck, its prongs vibrate. The forward motion creates a compression, and the backward motion creates a rarefaction. These travel through air to the listener's ear, causing the eardrum to vibrate, which is interpreted as sound. Similarly, when you pluck a stretched rubber band, you can see it vibrating and hear the humming sound it produces.
Key formulas:
- Speed of sound: v = f × λ (v = velocity, f = frequency, λ = wavelength)
- v ≈ 330 m/s in air at 0°C; ≈ 340 m/s at room temperature
- The speed of sound increases with temperature — roughly 0.6 m/s for every 1°C rise
Q2. Explain the factors affecting the loudness and pitch of sound. Answer: Loudness depends on: 1. Amplitude: Greater amplitude produces louder sound. When you strike a drum harder, the membrane vibrates with a larger amplitude, producing a louder sound. 2. Distance from source: Loudness decreases as distance from the source increases. This is because the energy of the sound wave spreads over a larger area as it moves outward. 3. Area of vibrating body: A larger vibrating area produces a louder sound. This is why a big drum produces a louder sound than a small drum when struck with the same force. 4. Density of medium: Sound is louder in denser media because more particles are available to transfer the energy of the vibration.
Pitch depends on: 1. Frequency: Higher frequency produces higher pitch (e.g., a whistle has high pitch, a drum has low pitch). A woman's voice generally has higher pitch than a man's voice because of higher frequency of vibration of the vocal cords. 2. Tension in string: Greater tension in a string produces higher pitch. This is why tightening a guitar string raises the pitch of the note it produces. 3. Thickness of string: Thinner strings produce higher pitch than thicker strings of the same material and tension. The high-pitch strings on a violin are thinner than the low-pitch ones. 4. Length of string: Shorter strings produce higher pitch. Pressing a string against a fret on a guitar shortens the vibrating length, raising the pitch.
Q3. Describe the human ear and its working. Answer: The human ear converts sound waves into electrical signals that the brain interprets. It has three parts:
1. Outer ear (Pinna): Collects sound waves from the air and directs them through the ear canal to the eardrum. The funnel-like shape of the pinna helps gather sound waves efficiently, and the ear canal amplifies the sound slightly as it travels toward the eardrum.
2. Middle ear: Contains the eardrum (tympanic membrane) and three tiny bones (hammer, anvil, stirrup) — the smallest bones in the human body. When sound waves hit the eardrum, it vibrates, and these vibrations are amplified about 20 times by the three bones and transmitted to the inner ear. The middle ear also connects to the throat via the Eustachian tube, which helps equalize pressure on both sides of the eardrum.
3. Inner ear (Cochlea): Contains fluid and thousands of microscopic hair cells. Vibrations from the middle ear create waves in the fluid, which stimulate the hair cells. These cells convert mechanical vibrations into electrical nerve impulses that travel via the auditory nerve to the brain, where they are interpreted as sound. The cochlea is coiled like a snail shell, and different parts respond to different frequencies — the base detects high frequencies and the apex detects low frequencies.
Q4. Explain with examples how sound travels through different media. Answer: Sound can travel through all three states of matter — solid, liquid, and gas — but at different speeds. The key factor is how closely the particles are packed: closer particles transfer vibrations more quickly.
1. Solid: Sound travels fastest in solids (e.g., iron: ~5,120 m/s). The closely packed particles quickly pass vibrations from one to the next. Example: If you put your ear to a railway track, you can hear a train approaching much earlier than through air. Another example: In old Western films, characters put their ear to the ground to detect approaching horses — sound travels faster through the ground than through air.
2. Liquid: Sound travels faster in liquids than in gases but slower than in solids (e.g., water: ~1,500 m/s). Example: Whales communicate over long distances using sound in water. Dolphins also use echolocation in water to locate objects and prey with remarkable precision.
3. Gas: Sound travels slowest in gases (e.g., air: ~330 m/s at 0°C). The particles are far apart, so vibrations take longer to transfer. Example: We hear thunder after seeing lightning because sound takes time to reach us through air. The speed of sound in air increases with temperature — roughly 340 m/s at room temperature.
Speed order: Solid > Liquid > Gas
Common Mistakes
- Confusing pitch with loudness: Pitch depends on frequency; loudness depends on amplitude. They are different properties.
- Saying sound travels fastest in air: Sound travels fastest in solids, not gases.
- Confusing frequency and time period: Frequency = 1/Time period. They are inversely related, not the same.
- Saying all vibrations produce audible sound: Infrasonic (< 20 Hz) and ultrasonic (> 20,000 Hz) vibrations are inaudible to humans.
- Confusing decibel with Hertz: Decibel (dB) measures loudness/intensity; Hertz (Hz) measures frequency.
- Forgetting to invert time period for frequency: If T = 0.02 s, then f = 1/T = 50 Hz, not 0.02 Hz.
- ❌ Thinking echo and reverberation are the same: ✅ An echo is a distinct, repeated sound heard when reflected sound reaches the ear at least 0.1 s after the original. Reverberation is the persistence of sound due to multiple rapid reflections that blend together, common in large halls.
- ❌ Assuming sound speed is constant in air: ✅ The speed of sound in air changes with temperature. At 0°C it is about 330 m/s, and it increases by roughly 0.6 m/s for every 1°C rise. Always check if the question specifies a temperature.
Exam Checklist
- [ ] Can you explain how sound is produced and propagated?
- [ ] Can you define frequency, amplitude, time period, and wavelength?
- [ ] Can you relate frequency to pitch and amplitude to loudness?
- [ ] Can you calculate frequency from time period (f = 1/T)?
- [ ] Can you list the speed of sound in solids, liquids, and gases?
- [ ] Can you describe the three types of musical instruments with examples?
- [ ] Can you explain why sound cannot travel through a vacuum?
- [ ] Can you distinguish between musical sound and noise?
- [ ] Can you describe the structure and working of the human ear?
- [ ] Can you explain ultrasonic and infrasonic sounds with uses?
- [ ] Can you define an echo and state the minimum distance needed to hear one?
- [ ] Can you explain how temperature affects the speed of sound in air?