Class 9 Science Sound
Class 9 Science Sound Fill in the blanks , Multiple Choice Questions and True false .
Fill in the Blanks
1. Sound is produced due to __________ of objects. Ans: vibration
2. Sound travels in the form of __________ waves. Ans: longitudinal
3. The region of high pressure in a sound wave is called __________. Ans: compression
4. The region of low pressure in a sound wave is called __________. Ans: rarefaction
5. The SI unit of frequency is __________. Ans: hertz (Hz)
6. Sound cannot travel in __________. Ans: vacuum
7. The distance between two consecutive compressions is called __________. Ans: wavelength
8. The time taken to complete one vibration is called __________. Ans: time period
9. Sound waves are also called __________ waves. Ans: mechanical
10. Loudness of sound depends on __________ of vibration. Ans: amplitude
11. The sensation of sound persists in our brain for about __________ seconds.
Ans: 0.1
12. __________ is the repeated reflection of sound in a big hall. Ans: Reverberation
13. The speed of sound is highest in __________. Ans: solids
14. Sounds below 20 Hz are called __________. Ans: infrasound
15. __________ is used to hear the heartbeat in the body. Ans: Stethoscope
Multiple Choice Questions
1. Sound travels fastest in:
a) Air
b) Water
c) Iron
d) Vacuum
Ans: c) Iron
2. The unit of amplitude is:
a) Hz
b) metre
c) second
d) Depends on quantity like pressure/density
Ans: d) Depends on quantity like pressure/density
3. Which one of these is a longitudinal wave?
a) Light
b) X-rays
c) Sound
d) Water waves
Ans: c) Sound
4. Pitch of sound depends on:
a) Amplitude
b) Frequency
c) Wavelength
d) Speed
Ans: b) Frequency
5. Echo is heard when the distance between source and reflector is at least:
a) 17.2 m
b) 10 m
c) 100 m
d) 1 m
Ans: a) 17.2 m
6. A sound wave of 500 Hz has time period:
a) 0.5 s
b) 2 s
c) 0.002 s
d) 5 s
Ans: c) 0.002 s
7. Which instrument is used to examine a foetus?
a) Megaphone
b) Microphone
c) Ultrasound scanner
d) Stethoscope
Ans: c) Ultrasound scanner
8. Infrasound has frequency:
a) Less than 20 Hz
b) Greater than 20 kHz
c) Between 20 Hz and 20 kHz
d) Exactly 100 Hz
Ans: a) Less than 20 Hz
9. The sound of a drum depends on:
a) Its size
b) Its material
c) Tension on the surface
d) All of the above
Ans: d) All of the above
10. Which part of human body vibrates to produce sound?
a) Ear
b) Nose
c) Vocal cords
d) Tongue
Ans: c) Vocal cords
11. Loudness is determined by:
a) Wavelength
b) Amplitude
c) Frequency
d) Speed
Ans: b) Amplitude
12. The speed of sound in air at 25°C is approx.:
a) 346 m/s
b) 331 m/s
c) 6400 m/s
d) 1200 m/s
Ans: a) 346 m/s
13. The process of bouncing back of sound is called:
a) Refraction
b) Reverberation
c) Reflection
d) Absorption
Ans: c) Reflection
14. Sound wave needs __________ to travel.
a) Light
b) Medium
c) Force
d) Vacuum
Ans: b) Medium
15. The sound you hear after thunder is delayed because:
a) Light travels faster than sound
b) Sound gets absorbed
c) Echo is formed
d) Sound takes a longer path
Ans: a) Light travels faster than sound
True or False
1. Sound needs a medium to travel. True
2. Sound can travel through vacuum. False
3. The human ear can hear all frequencies of sound. False
4. The speed of sound is more in solids than in gases. True
5. Echoes are heard when sound reflects off a surface. True
6. Sound travels faster in water than in iron. False
7. Amplitude of a wave determines its pitch. False
8. Frequency is measured in decibels. False
9. Sound waves are mechanical waves. True
10. Loudness increases with increase in amplitude. True
11. Hearing aids help people with hearing loss. True
12. Infrasound has a frequency more than 20 kHz. False
13. Reflection of sound is used in SONAR. True
14. The wavelength of a sound wave is the distance between two compressions. True
15. Reverberation is a form of sound absorption. False
