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Nature & Propagation of Sound — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Nature & Propagation of Sound MCQs with step-by-step solutions (10 questions). Part of Sound. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Nature & Propagation of Sound · medium · theory
Sound waves are:
A. electromagnetic waves
B. longitudinal mechanical waves that need a material medium ✓ Correct
C. transverse waves that travel through vacuum
D. waves that need no medium
Solution: Sound is a longitudinal mechanical wave; it needs particles of a medium (solid, liquid or gas) to travel.
Q2 — Nature & Propagation of Sound · hard · theory
An electric bell ringing inside a sealed glass jar becomes inaudible as air is pumped out. This shows that sound:
A. is an electromagnetic wave
B. needs light to travel
C. cannot travel through vacuum ✓ Correct
D. travels faster in vacuum
Solution: With no air (medium) there are no particles to carry the compressions and rarefactions, so sound cannot propagate.
Q3 — Nature & Propagation of Sound · hard · theory
Sound travels fastest in:
A. solids ✓ Correct
B. liquids
C. vacuum
D. gases
Solution: Particles are most tightly packed in solids, so sound travels fastest in solids and slowest in gases (and not at all in vacuum).
Q4 — Nature & Propagation of Sound · medium · numerical
Sound travels 1500 m in water in 1 s. The speed of sound in water is:
A. 150 m/s
B. 750 m/s
C. 15000 m/s
D. 1500 m/s ✓ Correct
Solution: Speed $= \dfrac{\text{distance}}{\text{time}} = \dfrac{1500}{1} = 1500$ m/s.
Q5 — Nature & Propagation of Sound · medium · theory
The regions of high pressure/density in a sound wave travelling through air are called:
A. crests
B. compressions ✓ Correct
C. rarefactions
D. troughs
Solution: In a longitudinal sound wave, compressions are high-density regions and rarefactions are low-density regions.
Q6 — Nature & Propagation of Sound · hard · numerical
Sound takes 3 s to travel from a source to a listener 1020 m away. The speed of sound in that air is:
A. 3060 m/s
B. 306 m/s
C. 1020 m/s
D. 340 m/s ✓ Correct
Solution: Speed $= \dfrac{1020}{3} = 340$ m/s.
Q7 — Nature & Propagation of Sound · easy · theory
Through which of the following can sound NOT travel?
A. A perfect vacuum ✓ Correct
B. Air in a room
C. A solid iron bar
D. Water in a tank
Solution: Sound is a mechanical wave and needs a material medium (solid, liquid or gas) to carry the vibrations. In a vacuum there are no particles to vibrate, so sound cannot travel.
Q8 — Nature & Propagation of Sound · easy · theory
When sound travels through air, the air particles vibrate back and forth along the same direction in which the wave moves. Such a wave is called a
A. Electromagnetic wave
B. Water surface wave
C. Longitudinal wave ✓ Correct
D. Transverse wave
Solution: In sound, particles of the medium oscillate parallel to the direction of wave travel, creating compressions and rarefactions. This makes sound a longitudinal wave.
Q9 — Nature & Propagation of Sound · medium · numerical
Sound travels at about 340 m/s in air. How long will it take to travel a distance of 1.02 km?
A. 3 s ✓ Correct
B. 6 s
C. 5 s
D. 2 s
Solution: Time = distance / speed. Distance = 1.02 km = 1020 m, so time = 1020 / 340 = 3 s.
Q10 — Nature & Propagation of Sound · hard · theory
A person strikes a long steel rail at one end. A listener standing at the other end hears the sound twice, once through the rail and once through the air. Which is heard first and why?
A. Through the rail first, because sound travels faster in solids than in gases ✓ Correct
B. Through the air first, because air is lighter than steel
C. Through the rail first, because the rail is longer than the air path
D. Both are heard at exactly the same instant
Solution: Solids are far more rigid (elastic) than gases and their particles are packed close together, so vibrations are passed on much faster. Sound therefore reaches the listener through the steel rail well before it arrives through the air.