Q1. easy
Sound is produced by objects that are:
- A Vibrating
- B Cold
- C Still
- D Coloured
Answer: A — Vibrating
Sound is produced by vibrating objects. A vibration is a rapid to-and-fro motion. When we stop the vibration, the sound stops too.
⚛️ Physics · Topic 9 of 10
Sound — Physics Questions with Answers
Start with the study notes on Sound (definitions, examples and a quick revision), then work through 60 practice questions, each with the correct answer and a clear explanation of why it is right. When you are ready, take this topic as an interactive quiz to test yourself.
Topic overview
Sound – vibrations we can hear
1. How is sound produced?
Sound is produced by vibrating objects. A vibration is a rapid to-and-fro movement. When the vibration stops, the sound stops.
Examples:
- Pluck a stretched rubber band, and you can see it blur as it vibrates.
- Touch a ringing bell, and the sound stops.
- A vibrating tuning fork dipped in water makes the water splash.
What vibrates in different sources
- Strings: guitar, sitar, violin.
- A stretched skin (membrane): tabla, dholak, drum.
- An air column: flute, whistle.
- Wings: buzzing bees and mosquitoes.
The human voice
We speak using the voice box (larynx) in our throat. Air from the lungs makes two vocal cords vibrate.
Example: Men usually have longer, thicker vocal cords, which vibrate more slowly and give a deeper voice.
2. Sound needs a medium
Sound travels as a wave: each vibrating particle passes the vibration on to the next. So sound needs a medium, which can be a solid, a liquid or a gas.
Sound cannot travel through a vacuum (empty space).
Example: Astronauts in space, or on the Moon, where there is no air, talk to each other by radio.
Speed of sound
Fastest in solids > liquids > slowest in gases
Examples:
- Put your ear to a long table and ask a friend to tap the far end. The sound is louder and clearer through the wood.
- We see lightning before we hear thunder, because light travels much faster than sound.
3. How we hear
Sound enters the ear and makes the eardrum, a thin stretched membrane, vibrate. These vibrations are passed on, and signals are sent to the brain.
4. Echo
An echo is a sound heard again after it reflects off a hard surface, such as a cliff or a large wall.
Example: Shouting in a large empty hall, or across a valley, gives an echo.
Soft materials absorb sound instead of reflecting it.
Examples:
- Curtains, carpets and foam are used in cinemas and studios to cut down echoes.
- A hall full of people echoes much less than an empty one.
5. Frequency and pitch
Frequency is the number of vibrations per second. It is measured in hertz (Hz).
Pitch is how shrill or deep a sound is. It depends on frequency:
- High frequency → high pitch (shrill): a whistle, a child's voice.
- Low frequency → low pitch (deep): a big drum, a man's voice.
6. Amplitude and loudness
Amplitude is how far a vibrating object moves from its resting position. Loudness depends on amplitude: the bigger the vibration, the louder the sound.
Loudness is measured in decibels (dB).
Examples:
- Hit a drum harder, and it sounds louder, but not higher.
- A whisper is about 30 dB, and normal talk about 60 dB.
Pitch depends on frequency · Loudness depends on amplitude
7. Sounds we can and cannot hear
Humans can hear sounds from about 20 Hz to 20,000 Hz. This is the audible range.
- Ultrasound: above 20,000 Hz. Bats use it to find insects in the dark, and doctors use it to see inside the body and check on unborn babies.
- Infrasound: below 20 Hz. Elephants and whales can use it.
Example: A dog whistle makes a sound too high for people to hear, but dogs hear it.
8. Noise and noise pollution
Noise is unwanted, unpleasant sound. Noise pollution is too much noise in our surroundings.
Long exposure to very loud sound, above about 80 dB, can damage hearing and cause stress, headaches and poor sleep.
Ways to reduce noise pollution:
- Silencers on vehicles and machines.
- Trees along roads to absorb sound.
- Ear protection for people who work in noisy places.
- Using horns and loudspeakers only when needed.
9. Common misconceptions
| Misconception | Correct understanding |
|---|---|
| Pitch and loudness are the same thing. | Pitch depends on frequency; loudness depends on amplitude. |
| Sound travels fastest in air. | It is fastest in solids and slowest in gases. |
| The hollow body of a guitar makes the sound. | The strings make the sound; the body makes it louder. |
| You could hear an explosion in space. | Space is a vacuum, so there is nothing to carry the sound. |
| Hitting a drum harder raises its pitch. | It makes the sound louder; the pitch stays about the same. |
10. Quick revision
- Vibration
- A rapid to-and-fro movement that produces sound.
- Medium
- A solid, liquid or gas that carries sound.
- Echo
- A sound reflected back from a hard surface.
- Frequency
- Vibrations per second, measured in hertz (Hz).
- Pitch
- How shrill or deep a sound is; set by frequency.
- Amplitude
- The size of a vibration; sets loudness.
- Audible range
- About 20 Hz to 20,000 Hz for humans.
- Ultrasound
- Sound above 20,000 Hz, too high for us to hear.
11. Test your understanding
What must happen for sound to be produced?
Show answer
Something must vibrate.
What vibrates in a flute?
Show answer
The air column inside it.
Why can't astronauts hear each other directly in space?
Show answer
Space is a vacuum, and sound needs a medium to travel.
In which medium does sound travel fastest?
Show answer
In solids.
Why do we see lightning before we hear thunder?
Show answer
Light travels much faster than sound.
What decides the pitch of a sound?
Show answer
Its frequency.
What happens to the sound when a drum is hit harder?
Show answer
The amplitude increases, so the sound becomes louder.
What is the audible range for humans?
Show answer
About 20 Hz to 20,000 Hz.
Key takeaway: Every sound starts as a vibration and needs a medium to travel. Frequency sets the pitch; amplitude sets the loudness.
Notes written by Velnov for Class 6–8 students, following the topics of the NCERT science syllabus.
Key concepts in this topic
Easy questions (2)
Q58. easy
Which of these is needed for sound to be produced?
- A A vibrating object
- B A magnet
- C Light
- D A vacuum
Answer: A — A vibrating object
Sound is always produced by a vibrating object - a plucked string, a struck drum, or vibrating vocal cords. Without vibration, there is no sound.
Medium questions (29)
Q2. medium
A rapid to-and-fro motion of an object is called:
- A Vibration
- B Rotation
- C Reflection
- D Refraction
Answer: A — Vibration
A vibration is a rapid back-and-forth (to-and-fro) movement. Vibrating objects like a plucked string, a drum's surface or a tuning fork produce sound.
Q3. medium
When you pluck a guitar string, you hear a sound because the string:
- A Vibrates
- B Gets hot
- C Changes colour
- D Becomes magnetic
Answer: A — Vibrates
Plucking makes the string vibrate rapidly, and these vibrations produce sound. If you touch and stop the string, the vibration and the sound both stop.
Q5. medium
The part of the body that vibrates to produce sound in a mosquito or a bee is:
- A Its wings (which beat/vibrate very fast)
- B Its legs
- C Its eyes
- D Its antennae
Answer: A — Its wings (which beat/vibrate very fast)
The buzzing of insects like mosquitoes and bees comes from the very fast vibration (beating) of their wings, which produces the humming sound.
Q8. medium
The bouncing back of sound from a hard surface (heard as a repeat of the original sound) is called an:
- A Echo
- B Refraction
- C Vibration
- D Vacuum
Answer: A — Echo
An echo is the reflection of sound from a hard surface (like a cliff or a big wall), heard shortly after the original sound. It is the reflection of sound.
Q10. medium
Which of these can our HUMAN EAR NOT do?
- A Hear a sound produced in a vacuum
- B Hear a bell in air
- C Hear sounds underwater
- D Hear through a solid wall
Answer: A — Hear a sound produced in a vacuum
Since sound cannot travel through a vacuum, no sound reaches our ears from a vacuum. We can hear sounds through air, water and solids, all of which are media that carry sound.
Q11. medium
The organ we use to HEAR sound is the:
- A Ear
- B Eye
- C Nose
- D Tongue
Answer: A — Ear
We hear sounds with our ears. Sound vibrations enter the ear, make the eardrum vibrate, and these signals are sent to the brain, which we perceive as sound.
Q14. medium
The unit of frequency is the:
- A Hertz (Hz)
- B Metre
- C Decibel
- D Newton
Answer: A — Hertz (Hz)
Frequency is measured in hertz (Hz). One hertz means one oscillation (vibration) per second. The pitch of a sound depends on its frequency.
Q16. medium
A whistle has a HIGH pitch and a drum has a LOW pitch. This difference is due to their different:
- A Frequencies
- B Amplitudes
- C Colours
- D Temperatures
Answer: A — Frequencies
A whistle vibrates at a high frequency, giving a shrill (high-pitched) sound. A drum vibrates at a low frequency, giving a deep (low-pitched) sound. Pitch is determined by frequency.
Q18. medium
The maximum distance a vibrating object moves from its rest position is called the:
- A Amplitude
- B Frequency
- C Pitch
- D Wavelength only
Answer: A — Amplitude
Amplitude is the maximum displacement of a vibrating object from its central (rest) position. A larger amplitude produces a louder sound.
Q20. medium
The loudness of sound is measured in units called:
- A Decibel (dB)
- B Hertz
- C Newton
- D Metre
Answer: A — Decibel (dB)
Loudness is measured in decibels (dB). A whisper is about 10-30 dB, normal talk about 60 dB, and very loud sounds (above 80 dB) can be harmful to the ears.
Q22. medium
Unwanted, unpleasant or disturbing sound is called:
- A Noise
- B Music
- C An echo
- D A vibration
Answer: A — Noise
Noise is unpleasant or unwanted sound (like traffic horns, machines, loudspeakers). Pleasant sounds (like from musical instruments) are called music.
Q24. medium
Which of these is a measure to REDUCE noise pollution?
- A Planting trees along roads and using silencers on machines/vehicles
- B Using louder horns
- C Playing loudspeakers all night
- D Bursting more crackers
Answer: A — Planting trees along roads and using silencers on machines/vehicles
Noise pollution can be reduced by planting trees (which absorb sound), using silencers on vehicles and machines, keeping horns and loudspeakers low, and moving noisy industries away from homes.
Q26. medium
Sound travels through air as the vibration is passed from one air particle to the next. This is why sound needs:
- A A medium (particles to carry the vibration)
- B Light
- C Electricity
- D A magnet
Answer: A — A medium (particles to carry the vibration)
Sound travels because vibrating particles pass their motion to neighbouring particles. Without a medium (particles), there is nothing to carry the vibration, so sound cannot travel through a vacuum.
Q28. medium
Which of these animals can hear sounds of much HIGHER frequency than humans?
- A Dogs and bats
- B Only humans
- C Fish only
- D No animal
Answer: A — Dogs and bats
Dogs, bats, dolphins and some other animals can hear ultrasonic sounds (very high frequencies) that humans cannot hear. Dog whistles use this - they make a high-pitched sound only dogs can hear.
Q30. medium
The audible range of frequencies for a normal human ear is about:
- A 20 Hz to 20,000 Hz
- B 0 Hz to 10 Hz
- C 100,000 Hz to 1,000,000 Hz
- D 1 Hz to 5 Hz
Answer: A — 20 Hz to 20,000 Hz
Humans can normally hear sounds with frequencies between about 20 Hz and 20,000 Hz. Below 20 Hz is infrasound and above 20,000 Hz is ultrasound - both inaudible to humans.
Q32. medium
A vibrating tuning fork placed in water will:
- A Splash the water (showing it is vibrating)
- B Freeze the water
- C Change the water's colour
- D Do nothing
Answer: A — Splash the water (showing it is vibrating)
A vibrating tuning fork touched to water splashes it, showing that the fork is vibrating. This is a common experiment to demonstrate that sound is produced by vibration.
Q34. medium
Two musical instruments playing the SAME note can still sound different because of their:
- A Quality (timbre) of sound
- B Loudness only
- C Colour
- D Weight
Answer: A — Quality (timbre) of sound
The quality (timbre) of a sound lets us tell instruments apart even when they play the same note at the same loudness. This is why a flute and a violin sound different playing the same note.
Q36. medium
Which of the following produces sound by the vibration of a stretched membrane?
- A A drum (tabla)
- B A flute
- C A guitar
- D A whistle
Answer: A — A drum (tabla)
A drum (like a tabla or dholak) produces sound when its stretched membrane (skin) vibrates on being struck. A flute uses vibrating air columns, and a guitar uses vibrating strings.
Q38. medium
Which of the following is TRUE about the speed of sound compared to the speed of light?
- A Sound travels much slower than light
- B Sound travels faster than light
- C They travel at the same speed
- D Neither has a speed
Answer: A — Sound travels much slower than light
Sound travels much slower than light. That is why in a thunderstorm we see the lightning flash first and hear the thunder a few seconds later, even though both happen at the same time.
Q40. medium
Which part of a guitar vibrates to produce sound?
- A The strings
- B The wooden box only
- C The colour
- D The tuning pegs
Answer: A — The strings
The vibrating strings of a guitar produce the sound. The hollow wooden box amplifies (makes louder) the sound, but the source of the vibration is the strings.
Q42. medium
A large empty hall produces echoes, but a hall full of people and furniture does not, because:
- A People and soft furnishings absorb the sound, reducing reflection
- B People make the sound louder
- C Furniture reflects all sound
- D Empty halls have no walls
Answer: A — People and soft furnishings absorb the sound, reducing reflection
In an empty hall, hard walls reflect sound, producing echoes. People, clothes and soft furnishings absorb much of the sound, so there is less reflection and fewer echoes.
Q44. medium
Which statement about amplitude and loudness is CORRECT?
- A Larger amplitude produces louder sound
- B Larger amplitude produces softer sound
- C Amplitude does not affect loudness
- D Loudness depends on frequency
Answer: A — Larger amplitude produces louder sound
Loudness increases with amplitude. The larger the vibration (amplitude), the louder the sound. Pitch, by contrast, depends on frequency, not amplitude.
Q46. medium
Which of these is NOT a musical instrument that works by vibration?
- A None - all musical instruments work by vibration
- B A drum
- C A violin
- D A flute
Answer: A — None - all musical instruments work by vibration
All musical instruments produce sound through vibration - drums by vibrating membranes, string instruments by vibrating strings, and wind instruments by vibrating air columns. So none of them work without vibration.
Q48. medium
Which of these is an example of noise pollution?
- A Loud vehicle horns and blaring loudspeakers
- B Soft instrumental music
- C Birds chirping gently
- D A quiet conversation
Answer: A — Loud vehicle horns and blaring loudspeakers
Loud horns, blaring loudspeakers, factory machines and bursting crackers are sources of noise pollution - unwanted, loud sounds that disturb and harm us. Gentle, pleasant sounds are not noise pollution.
Q50. medium
Sound is a form of:
- A Energy
- B Matter
- C Force
- D Light
Answer: A — Energy
Sound is a form of energy that travels as waves through a medium. It can do work - for instance, loud sound can rattle windows - showing it carries energy.
Q52. medium
When the vibration of an object stops, the sound it produces:
- A Also stops
- B Becomes louder
- C Continues forever
- D Changes colour
Answer: A — Also stops
Sound is produced only while an object vibrates. As soon as the vibration stops (for example, when you touch a ringing bell), the sound stops too.
Q54. medium
A telephone or mobile phone converts sound into ______ to send it far, then back into sound at the other end.
- A Electrical signals
- B Light only
- C Heat
- D Magnetism only
Answer: A — Electrical signals
A phone converts sound (your voice) into electrical (and radio) signals that travel quickly over long distances. At the other end, these signals are converted back into sound so the listener can hear you.
Q56. medium
Why can we hear each other's voices in a room but not through a thick, sealed vacuum chamber?
- A Air in the room carries the sound, but a vacuum has no medium to carry it
- B The room is warmer
- C The vacuum absorbs light
- D Voices are magnetic
Answer: A — Air in the room carries the sound, but a vacuum has no medium to carry it
The air in the room acts as a medium that carries sound vibrations to our ears. A vacuum has no air (no medium), so sound cannot travel through it, and we cannot hear.
Q59. medium
Two sounds have the same loudness but different pitch. They differ in their:
- A Frequency
- B Amplitude
- C Loudness
- D Colour
Answer: A — Frequency
Pitch depends on frequency. If two sounds are equally loud (same amplitude) but one is higher-pitched, they must have different frequencies.
Hard questions (29)
Q4. hard
In humans, sound is produced by the voice box (larynx), which contains:
- A Vocal cords that vibrate as air passes through
- B A drum
- C A magnet
- D A string
Answer: A — Vocal cords that vibrate as air passes through
The human voice box (larynx) has two vocal cords with a slit between them. When we speak, air from the lungs passes through and makes the vocal cords vibrate, producing sound.
Q6. hard
Sound needs a MEDIUM (such as air, water or a solid) to travel. This means sound CANNOT travel through:
- A A vacuum (empty space)
- B Air
- C Water
- D Iron
Answer: A — A vacuum (empty space)
Sound requires a material medium (solid, liquid or gas) to travel, because it moves as vibrations passed from particle to particle. In a vacuum (like outer space), there are no particles, so sound cannot travel.
Q7. hard
In which medium does sound travel FASTEST?
- A In solids
- B In liquids
- C In gases (air)
- D In a vacuum
Answer: A — In solids
Sound travels fastest in solids (particles are tightly packed), slower in liquids, and slowest in gases like air. It cannot travel in a vacuum at all. That is why you can hear a train coming by putting your ear to the rail.
Q9. hard
An echo is caused by the ______ of sound.
- A Reflection
- B Absorption
- C Vibration only
- D Refraction
Answer: A — Reflection
An echo is produced when sound reflects (bounces back) off a distant hard surface and returns to our ears. We hear the reflected sound as a repeat of the original.
Q12. hard
The thin, stretched membrane in the ear that vibrates when sound falls on it is the:
- A Eardrum (tympanic membrane)
- B Retina
- C Vocal cord
- D Cornea
Answer: A — Eardrum (tympanic membrane)
The eardrum is a thin, tightly stretched membrane. Sound vibrations make it vibrate, and these vibrations are passed on through the ear to the inner ear and then, as signals, to the brain.
Q13. hard
The number of vibrations (oscillations) made in ONE SECOND is called the:
- A Frequency
- B Amplitude
- C Time period
- D Speed
Answer: A — Frequency
Frequency is the number of oscillations per second. Its unit is the hertz (Hz). Higher frequency means a shriller (higher-pitched) sound.
Q15. hard
The 'PITCH' of a sound (how shrill or how deep it sounds) depends on its:
- A Frequency (higher frequency = higher pitch)
- B Amplitude
- C Colour
- D Temperature
Answer: A — Frequency (higher frequency = higher pitch)
Pitch depends on frequency. A high-frequency sound has a high pitch (shrill, like a whistle or a child's voice), and a low-frequency sound has a low pitch (deep, like a drum or a man's voice).
Q17. hard
The 'LOUDNESS' of a sound depends on its:
- A Amplitude (the size of the vibration)
- B Frequency
- C Colour
- D Speed
Answer: A — Amplitude (the size of the vibration)
Loudness depends on amplitude - the larger the amplitude of the vibration, the louder the sound. Hitting a drum harder gives a larger amplitude and a louder sound.
Q19. hard
If you strike a drum HARDER, the sound becomes:
- A Louder (because the amplitude increases)
- B Higher in pitch
- C Softer
- D Lower in pitch
Answer: A — Louder (because the amplitude increases)
Striking harder makes the drum's surface vibrate with a larger amplitude, producing a louder sound. (The pitch, which depends on frequency, stays about the same.)
Q21. hard
Sounds of very high loudness (above about 80 dB) are harmful because they can:
- A Damage hearing and cause stress
- B Improve eyesight
- C Make us stronger
- D Have no effect
Answer: A — Damage hearing and cause stress
Prolonged exposure to very loud sounds can damage the delicate eardrum and hearing, and cause stress, headaches, sleeplessness and other health problems.
Q23. hard
The presence of excessive or unwanted sounds in the environment is called:
- A Noise pollution
- B Air pollution
- C Water pollution
- D Soil pollution
Answer: A — Noise pollution
Noise pollution is the presence of too much unwanted, loud sound in the surroundings (from traffic, factories, loudspeakers, crackers). It harms health, so it should be reduced.
Q25. hard
Pleasant sounds (as from musical instruments and singing) are called:
- A Music
- B Noise
- C Echoes
- D Vibrations only
Answer: A — Music
Music is pleasant, agreeable sound produced by musical instruments and singing. Noise, in contrast, is unpleasant or disturbing sound.
Q27. hard
You can hear an approaching train earlier by putting your ear on the rail rather than listening through the air because:
- A Sound travels faster and better through solids (the steel rail) than through air
- B Rails are magnetic
- C Air blocks all sound
- D The rail produces the sound
Answer: A — Sound travels faster and better through solids (the steel rail) than through air
Sound travels much faster and more efficiently through solids like the steel rail than through air. So the sound of the distant train reaches your ear sooner and more clearly through the rail.
Q29. hard
Sounds with frequencies ABOVE the range of human hearing (above about 20,000 Hz) are called:
- A Ultrasonic sounds (ultrasound)
- B Infrasonic sounds
- C Audible sounds
- D Noise
Answer: A — Ultrasonic sounds (ultrasound)
Ultrasonic sounds (ultrasound) have frequencies above 20,000 Hz - too high for humans to hear. They are used in medical scans (ultrasound imaging), cleaning, and by animals like bats and dolphins.
Q31. hard
Sounds with frequencies BELOW the range of human hearing (below about 20 Hz) are called:
- A Infrasonic sounds (infrasound)
- B Ultrasonic sounds
- C Audible sounds
- D Echoes
Answer: A — Infrasonic sounds (infrasound)
Infrasonic sounds (infrasound) have frequencies below 20 Hz, too low for humans to hear. Some animals like elephants and whales can produce and hear infrasound.
Q33. hard
When a sound is produced in air, the vibrations create regions of high and low pressure that travel outward. Sound therefore travels as a:
- A Wave
- B Straight solid rod
- C Ray of light
- D Magnetic field
Answer: A — Wave
Sound travels as a wave - a disturbance that passes through the medium as alternating compressions (high pressure) and rarefactions (low pressure), carrying energy from the source to our ears.
Q35. hard
Why is there NO sound on the Moon (even if two astronauts stand close and shout)?
- A The Moon has no atmosphere (no air), and sound cannot travel without a medium
- B The Moon is too cold
- C Sound is absorbed by moon dust
- D Astronauts cannot speak
Answer: A — The Moon has no atmosphere (no air), and sound cannot travel without a medium
The Moon has no air (no medium) to carry sound. Since sound needs a material medium to travel, astronauts cannot hear each other directly and must use radios (which use electromagnetic waves) to talk.
Q37. hard
In a FLUTE, the sound is produced by the vibration of:
- A The air column inside it
- B A stretched string
- C A membrane
- D A metal rod
Answer: A — The air column inside it
A flute produces sound by the vibration of the air column inside it when you blow across it. Changing the length of the vibrating air column (by covering holes) changes the pitch.
Q39. hard
During a thunderstorm, we see lightning BEFORE we hear thunder because:
- A Light travels much faster than sound
- B Thunder comes after lightning
- C Sound travels faster than light
- D Lightning is louder
Answer: A — Light travels much faster than sound
Lightning and thunder occur together, but light travels far faster than sound. So the light reaches us almost instantly, while the sound of thunder takes longer, arriving a few seconds later.
Q41. hard
Soft materials like curtains, carpets and foam are used in recording studios and cinema halls to:
- A Absorb sound and reduce echoes
- B Increase echoes
- C Make sound travel faster
- D Produce sound
Answer: A — Absorb sound and reduce echoes
Soft, porous materials absorb sound rather than reflecting it. Using them on walls reduces unwanted echoes and reverberation, giving clearer sound - useful in studios, theatres and auditoriums.
Q43. hard
Which statement about frequency and pitch is CORRECT?
- A Higher frequency produces higher pitch; lower frequency produces lower pitch
- B Higher frequency produces lower pitch
- C Frequency does not affect pitch
- D Pitch depends on loudness
Answer: A — Higher frequency produces higher pitch; lower frequency produces lower pitch
Pitch increases with frequency. A high-frequency vibration gives a high-pitched (shrill) sound; a low-frequency vibration gives a low-pitched (deep) sound. Loudness, by contrast, depends on amplitude.
Q45. hard
A man's voice is usually DEEPER (lower pitch) than a child's voice because the man's vocal cords:
- A Are longer/thicker and vibrate at a lower frequency
- B Vibrate at a higher frequency
- C Do not vibrate
- D Are made of a different material
Answer: A — Are longer/thicker and vibrate at a lower frequency
Men generally have longer and thicker vocal cords, which vibrate at a lower frequency, giving a deeper (lower-pitched) voice. Children and women often have shorter vocal cords, giving higher-pitched voices.
Q47. hard
Bats fly in the dark and catch insects using:
- A Ultrasonic sounds (they emit ultrasound and detect the echoes)
- B Their eyes in the dark
- C Magnets
- D Their sense of smell only
Answer: A — Ultrasonic sounds (they emit ultrasound and detect the echoes)
Bats emit high-frequency ultrasonic sounds and listen for the echoes bouncing off objects and insects. From the echoes they judge distance and direction, navigating and hunting in complete darkness (echolocation).
Q49. hard
Which of the following correctly matches the property of sound with what it depends on?
- A Pitch - frequency; Loudness - amplitude
- B Pitch - amplitude; Loudness - frequency
- C Pitch - colour; Loudness - speed
- D Pitch - temperature; Loudness - frequency
Answer: A — Pitch - frequency; Loudness - amplitude
Pitch depends on frequency (higher frequency = higher pitch), and loudness depends on amplitude (larger amplitude = louder sound). Getting these two right is a very common exam point.
Q51. hard
To reduce the harmful effect of noise, machines in factories are fitted with silencers and workers may wear:
- A Ear protectors (earmuffs/earplugs)
- B Sunglasses
- C Gloves only
- D Helmets for the eyes
Answer: A — Ear protectors (earmuffs/earplugs)
Workers in noisy places wear ear protectors (earmuffs or earplugs) to protect their hearing from loud, harmful sound. Machines are also fitted with silencers to reduce the noise they make.
Q53. hard
Which correctly lists the media in order of DECREASING speed of sound?
- A Solid > Liquid > Gas
- B Gas > Liquid > Solid
- C Liquid > Solid > Gas
- D Gas > Solid > Liquid
Answer: A — Solid > Liquid > Gas
Sound travels fastest in solids, slower in liquids, and slowest in gases, because particles are most tightly packed in solids and can pass on the vibration quickest. It does not travel in a vacuum.
Q55. hard
Which overall statement about sound is CORRECT?
- A Sound is produced by vibration, needs a medium to travel, and its pitch depends on frequency while loudness depends on amplitude
- B Sound can travel through a vacuum
- C Loudness depends on frequency
- D Sound is not a form of energy
Answer: A — Sound is produced by vibration, needs a medium to travel, and its pitch depends on frequency while loudness depends on amplitude
Sound is produced by vibrating objects, travels as waves through a medium (solid, liquid or gas, but not a vacuum), and is a form of energy. Its pitch depends on frequency and its loudness on amplitude.
Q57. hard
Ultrasound is used in hospitals mainly to:
- A Make images of internal organs and unborn babies (ultrasound scan)
- B Heat the patient
- C Measure blood pressure
- D Produce X-rays
Answer: A — Make images of internal organs and unborn babies (ultrasound scan)
Ultrasound (high-frequency sound above 20,000 Hz) is used in medical scans to make images of internal organs and to check the health of an unborn baby, without the harmful radiation of X-rays.
Q60. hard
Why can astronauts on a spacewalk NOT hear each other directly, even shouting?
- A Space is a vacuum with no medium to carry sound
- B Their helmets are soundproof by design only
- C Sound travels too fast in space
- D They cannot open their mouths
Answer: A — Space is a vacuum with no medium to carry sound
Outer space is a vacuum - there is no air (medium) to carry sound vibrations. So astronauts cannot hear each other directly and must communicate using radios, which use electromagnetic waves (not sound) that can travel through a vacuum.