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Science Assertion (A) & Reason (B) MCQ

Sound · Jharkhand Board (JAC) STD 9 (Jharkhand - English Medium). 5 questions.

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Assertion (A) & Reason (B) MCQ

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5 questions · timed · auto-graded

MCQ 11 Mark
In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
Assertion: $SONAR$ sound cannot be audible to human ear inside water.
Reason: Human ears are able to sense ultrasonic sound as it has high frequency.
  • A
    Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
  • B
    The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
  • ✓
    Assertion is true but the Reason is false.
  • D
    The statement of the Assertion is false but the Reason is true.
Answer
Correct option: C.
Assertion is true but the Reason is false.

When a sound travels through a liquid it has to move though a thicker substance. This means that the sound has more difficulty causing the vibrations. So, although sound travels better in water, it is harder to hear properly.
Ultrasound is nothing but sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is no different from 'normal' (audible) sound in its physical properties, except in that humans cannot hear it.
Hence, Ultrasound which has a range of above $20kHz$ $(20,000\ Hz)$ can't be heard.

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MCQ 21 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as
Assertion: Ultrasonic sound is used in industry for detecting flaws (cracks etc) in metal blocks without damaging them.
Reason: An internal crack (or hole) does not allow ultrasound to poss through it.
  • ✓
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • C
    If Assertion is true, but Reason is false.
  • D
    If Assertion is false, but Reason is true.
Answer
Correct option: A.
If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Ultrasounds can be used to detect cracks and flaws in metal blocks. Ultrasonic waves are allowed to pass through the metallic block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.

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MCQ 31 Mark
In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
Assertion: Sound produced on the stage of a hall should spread uniformly across the hall.
Reason: Reflection of sound does not occur from polished or smooth surfaces.
  • A
    Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
  • B
    The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
  • ✓
    Assertion is true but the Reason is false.
  • D
    The statement of the Assertion is false but the Reason is true.
Answer
Correct option: C.
Assertion is true but the Reason is false.
For hearing a distinct sound, the time interval between the original sound and the reflected one must be at least $0.1s$. The persistence of sound in an auditorium is the result of repeated reflections of sound and is called reverberation.
Because if the surface of the mirror is not smooth, then the laws of reflection would not work, that due to rough surface the angle of incidence is not always equal to of reflection. Thus it is very necessary to have a smooth reflecting surface to study the laws of reflection of sound.
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MCQ 41 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as:
Assertion: Sound wave is an electromagnetic wave.
Reason: Speed of sound in solid is less than air.
  • A
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • C
    If Assertion is true, but Reason is false.
  • ✓
    If Assertion and Reason both are false.
Answer
Correct option: D.
If Assertion and Reason both are false.
Speed of the sound depends on the medium through which it is traveling. Speed travels faster in solids than liquids and gases. Speed of sound means velocity of the sound wave(pressure wave with infinitesimal strength) in that medium.
Sound waves are examples of mechanical waves while light waves are examples of electromagnetic waves. Electromagnetic waves are created by the vibration of an electric charge.
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MCQ 51 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as
Assertion: The loudness of sound is measured in decibel.
Reason: If sound waves have a large amplitude then the sound will be loud.
  • ✓
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • C
    If Assertion is true, but Reason is false.
  • D
    If Assertion is false, but Reason is true.
Answer
Correct option: A.
If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
As the amplitude of the sound wave increases, the intensity of the sound increases. Sounds with higher intensities are perceived to be louder. Relative sound intensities are often given in units named decibels (dB).
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Assertion (A) & Reason (B) MCQ - Science STD 9 Questions - Vidyadip