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Echo & Reverberation — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Echo & Reverberation 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 — Echo & Reverberation · medium · theory
An echo is heard because sound is:
A. transmitted through the obstacle
B. absorbed by the obstacle
C. reflected back from a distant obstacle ✓ Correct
D. refracted through the air
Solution: An echo is the repetition of a sound caused by its reflection from a surface.
Q2 — Echo & Reverberation · hard · numerical
A person shouts towards a cliff and hears the echo after 3 s. If the speed of sound is 340 m/s, the distance of the cliff is:
A. 113 m
B. 1020 m
C. 340 m
D. 510 m ✓ Correct
Solution: Sound travels to the cliff and back: total distance $= 340 \times 3 = 1020$ m, so the cliff is $\dfrac{1020}{2} = 510$ m away.
Q3 — Echo & Reverberation · hard · theory
To hear a distinct echo, the reflecting surface must be at least about 17 m away because:
A. echoes need bright light
B. the surface must be very hard
C. sound travels very slowly
D. the ear can distinguish two sounds separated by at least 0.1 s ✓ Correct
Solution: The ear resolves sounds ~0.1 s apart; in 0.1 s sound travels 34 m (there and back), so the surface must be at least ~17 m away.
Q4 — Echo & Reverberation · medium · theory
The persistence of sound in a large hall due to repeated reflections is called:
A. diffraction
B. refraction
C. an echo
D. reverberation ✓ Correct
Solution: Reverberation is the prolonging of sound by multiple reflections before it dies out.
Q5 — Echo & Reverberation · medium · theory
The ceilings and walls of cinema halls are made of sound-absorbing materials to:
A. reduce reverberation ✓ Correct
B. reflect all sound
C. increase reverberation
D. increase the echo
Solution: Absorbing materials cut down repeated reflections, reducing reverberation so speech is clear.
Q6 — Echo & Reverberation · hard · numerical
A ship sends an ultrasound pulse to the sea bed and receives the echo after 2 s. If the speed of sound in water is 1500 m/s, the depth of the sea is:
A. 1500 m ✓ Correct
B. 1000 m
C. 750 m
D. 3000 m
Solution: Total path $= 1500 \times 2 = 3000$ m; depth $= \dfrac{3000}{2} = 1500$ m (this method is SONAR).
Q7 — Echo & Reverberation · easy · theory
An echo is produced because of which property of sound?
A. Reflection of sound ✓ Correct
B. Diffraction of sound
C. Absorption of sound
D. Refraction of sound
Solution: An echo is simply the original sound heard again after it bounces back from a distant surface. This bouncing back is reflection of sound.
Q8 — Echo & Reverberation · medium · numerical
A person claps once and hears the echo from a cliff after 3 s. Taking the speed of sound as 340 m/s, how far away is the cliff?
A. 510 m ✓ Correct
B. 340 m
C. 1020 m
D. 255 m
Solution: In 3 s the sound travels to the cliff and back: total distance = 340 x 3 = 1020 m. The cliff is half of this, 1020 / 2 = 510 m away.
Q9 — Echo & Reverberation · hard · numerical
The ear can tell an echo apart from the original sound only if they are separated by at least 0.1 s. At a sound speed of 340 m/s, what is the minimum distance of a reflecting wall for a distinct echo to be heard?
A. 17 m ✓ Correct
B. 8.5 m
C. 3.4 m
D. 34 m
Solution: In 0.1 s sound covers 340 x 0.1 = 34 m, but this is the to-and-fro path. The wall must therefore be at least 34 / 2 = 17 m away.
Q10 — Echo & Reverberation · hard · theory
In a large empty hall, sound seems to persist for a while even after the source stops. Hanging thick curtains and laying carpets reduces this effect. The persistence of sound is called ___ and the curtains help by ___.
A. resonance; amplifying the sound
B. refraction; bending the sound
C. reverberation; absorbing the sound ✓ Correct
D. echo; reflecting the sound better
Solution: Repeated reflections from bare hard walls make sound linger; this is reverberation. Soft porous materials such as curtains and carpets absorb sound energy, cutting down the reflections and the persistence.