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Sound — Class 9 CBSE Science MCQs with Solutions
Free Class 9 CBSE Science Sound MCQs with step-by-step solutions. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — easy
Sound waves are produced by vibrating objects and are classified as:
A. Transverse waves
B. Longitudinal mechanical waves ✓ Correct
C. Electromagnetic waves
D. Surface radio waves
Solution: Sound requires a medium and propagates via longitudinal compressions and rarefactions.
Q2 — easy
Sound CANNOT travel through:
A. Solids
B. Liquids
C. Gases
D. Vacuum ✓ Correct
Solution: Sound is a mechanical wave requiring a material medium.
Q3 — easy
Distance between two consecutive compressions or two consecutive rarefactions is:
A. Amplitude
B. Wavelength (λ) ✓ Correct
C. Frequency
D. Time period
Solution: Wavelength λ is the spatial period of a wave.
Q4 — easy
Number of complete wave oscillations passing per unit time is called:
A. Wavelength
B. Frequency (ν) ✓ Correct
C. Amplitude
D. Speed
Solution: Frequency is measured in Hertz (Hz).
Q5 — easy
SI unit of frequency of a sound wave is:
A. Decibel (d
B. B) Hertz (Hz) ✓ Correct
C. Metre (m)
D. Second (s)
Solution: 1 Hertz = 1 oscillation per second.
Q6 — easy
Loudness of sound depends primarily on wave's:
A. Frequency
B. Amplitude ✓ Correct
C. Speed
D. Wavelength
Solution: Loudness is proportional to square of amplitude.
Q7 — easy
Pitch or shrillness of a sound depends on its:
A. Amplitude
B. Frequency ✓ Correct
C. Speed
D. Energy
Solution: Higher frequency produces higher pitch.
Q8 — easy
Audible frequency range for normal human ear is approximately:
A. 0 Hz to 100 Hz
B. 20 Hz to 20,000 Hz (20 kHz) ✓ Correct
C. Above 20,000 Hz
D. Below 20 Hz
Solution: Human hearing spans 20 Hz to 20 kHz.
Q9 — easy
Sound waves having frequency BELOW 20 Hz are called:
A. Ultrasound
B. Infrasound (Infrasonic) ✓ Correct
C. Audible sound
D. Supersonic
Solution: Infrasound frequencies are below 20 Hz (e.g. earthquakes, elephants).
Q10 — easy
Sound waves having frequency ABOVE 20,000 Hz (20 kHz) are called:
A. Infrasound
B. Ultrasound (Ultrasonic) ✓ Correct
C. Audible range
D. Subsonic
Solution: Ultrasound frequencies exceed 20,000 Hz (e.g. bats, medical SONAR).
Q11 — easy
Speed of sound is MAXIMUM in _______ and MINIMUM in _______.
A. Gases, Solids
B. Solids, Gases ✓ Correct
C. Liquids, Solids
D. Vacuum, Liquids
Solution: Sound travels fastest in dense solids (~5000 m/s in iron) and slowest in gases (~343 m/s in air).
Q12 — easy
Persistence of sound in a big hall due to repeated reflections from walls is:
A. Echo
B. Reverberation ✓ Correct
C. Refraction
D. Resonance
Solution: Reverberation is prolonged sound persistence due to multiple reflections.
Q13 — easy
Minimum distance between sound source and reflecting surface to hear a distinct echo in air is about: (speed of sound = 340 m/s)
A. 17.2 metres ✓ Correct
B. 34.4 metres
C. 50 metres
D. 10 metres
Solution: Time lag = 0.1 s → Total distance = 34 m → One-way distance = 17.2 m.
Q14 — easy
Technique using ultrasonic waves to measure ocean depth or locate underwater objects is:
A. RADAR
B. SONAR (Sound Navigation and Ranging) ✓ Correct
C. LASER
D. ECG
Solution: SONAR utilizes ultrasonic pulses and echo timing.
Q15 — medium
Speed of sound (v), frequency (ν), and wavelength (λ) are related by equation:
A. v = ν × λ ✓ Correct
B. v = ν / λ
C. v = λ / ν
D. v = ν + λ
Solution: Wave velocity v = frequency ν × wavelength λ.