HOTS Questions: Sound - Class 9 MCQ

The upward movement from mean position is called crest and downward movement is called troughs. The crest and trough are the parts of a transverse wave. The wavelength of the wave is a combination of the crest and trough. 

Speed of sound is different at different temperature. with increase in temperature, speed of sound increases. Loudness of sound is measured in decibels.

Speed of sound in aluminum = 6420 m /s
Speed of sound in water = 1520 m /s 
Speed of sound in air at 25° C = 347 m/s
Speed of sound in oxygen gas = 328 m/s

The principle of reflection of sound is used in megaphone, sound boards and stethoscope and other instruments.

X-rays, light rays are electrostatic waves. These waves do not require material medium for its propagation.

Frequency of infrasonic waves is less than frequency of ultrasound waves. Frequency of infrasonic waves are less than 20Hz and frequency of ultrasonic waves are greater than 20,000Hz.

Ultrasound waves vibrate at frequency higher than 20,000Hz. Vibration at such a high speed can be used to breaking and cutting objects like stone in kidney.

The correct option is B.

Echo -  the repetition of a sound caused by reflection of sound waves.

A reverberation, or reverb, is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air. 

Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. 

The concave surface of the sound board reflects the sound waves of the speaker towards the audience and hence prevents the spreading of sound in various directions. Due to this, sound is distributed uniformly throughout the hall and even the persons sitting at the back of the hall can hear the speech easily.

Sound wave propagates as compressions & rarefactions in the medium. Sound waves are longitudinal waves.

The range of hearing of normal human being is form 20 Hz to 20,000Hz. This range is called as audible range of human beings.
upper limit means the higher value

both A and B

Explanation:

• Statement A: Human beings are ultrasound deaf – This is true. Humans can hear sounds in the frequency range of approximately 20 Hz to 20,000 Hz. Ultrasound refers to sound waves with frequencies higher than 20,000 Hz, which are beyond the hearing range of humans.

• Statement B: Ultrasonic waves can travel easily in solid, liquid, and gases – This is also true. Ultrasonic waves can propagate through all three states of matter (solid, liquid, and gas), although their speed and behavior differ in each medium. They typically travel faster in solids compared to liquids and gases.

The maximum displacement from the particle of the mean position is called the Amplitude. Loudness of sound depends upon amplitude.

The wavelength is the distance between two consecutive crest or trough in case of transverse wave. Here, distance between consecutive crest and trough is x, so, wavelength will be 2x.

Two conditions for echo to be heard are as follows:-

1. 17 m minimum distance should be there.
2. Persistence of hearing is 0.1 secor minimum time gap between two sounds is 1/10 second.
    

Loudness of sound depends upon amplitude. Amplitude is the maximum displacement from mean position.

Children can hear sound of frequency up to 25,000Hz which is more than normal adult hearing range.

The correct option is D.
Animals such as bats,tortoises, dogs  and dolphins send out ultrasound waves and use their echoes, or reflected waves, to identify the locations of objects they cannot see. This is called echolocation. Animals use echolocation to find prey and avoid running into objects in the dark.

The eardrum is a stretched membranous structure at the junction of outer ear and middle ear. Vibration of eardrum causes production of sound that we hear.

There are 20 crests and 20 trough in 0.2s, which implies 20 waves.

And if there are 20 crests and 20 trough, this mean that there are 20 waves in 0.2s

∴ Frequency= Number of waves/ Time taken

=20/0.2=200/2 = 100Hz

∴ν = 100Hz

Option (C) is the correct answer.

Speed = distance/time, 10m/0.05s = 200m/s. wavelength = wave speed / frequency = 200 ms⁻¹/200Hz = 1m.

Speed of sound = 344m/s. time taken to hear echo = 0.1s. 2×distance0.1s. 2×distance = speed×time. 2×d =344×0.1 = 34.4 m. d = 17.2m.

Cochlea, semicircular canals and auditory nerve are associated with inner ear.

Wave motion shifts wave energy from one region to another region. Mass is not transferred during wave motion.