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NCERT Exemplar · Class 9 Science Sound

20 questions · 20 still being checked

Multiple Choice Questions 1–9 (part 1 of 3)

  1. Exercise 1

    Note is a sound
    (a)
    of mixture of several frequencies
    (b)
    of mixture of two frequencies only
    (c)
    of a single frequency
    (d)
    always unpleasant to listen

    Check this one against your book

    NCERT’s printed answer for this exercise does not match its own question. This working follows the question as printed.

    (a) A mixture of several frequencies. A single frequency is a tone; blending several frequencies together, with a common fundamental, gives the richer, pleasant sound of a note.NCERT prints: (c) — but (c) is a single frequency, the definition of a tone; the textbook's own definition of a note is a mixture of several frequencies, option (a).

  2. Exercise 2

    A key of a mechanical piano struck gently and then struck again but much
    harder this time. In the second case
    (a)
    sound will be louder but pitch will not be different
    (b)
    sound will be louder and pitch will also be higher
    (c)
    sound will be louder but pitch will be lower
    (d)
    both loudness and pitch will remain unaffected

    Matches the book, not yet reviewed

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    NCERT’s answer
    (a)
    (a) Louder, but the same pitch.Striking harder only raises the string's amplitude; its frequency, fixed by length and tension, is unchanged, so the pitch stays the same.Answer: (a) louder, same pitch.

  3. Exercise 3

    In SONAR, we use
    (a)
    ultrasonic waves
    (b)
    infrasonic waves
    (c)
    radio waves
    (d)
    audible sound waves

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (a)
    (a) Ultrasonic waves. Their short wavelength gives a narrow, directional beam that reflects sharply off the target, so the timed echo fixes range and direction precisely.Answer: (a) ultrasonic waves.

  4. Exercise 4

    Sound travels in air if
    (a)
    particles of medium travel from one place to another
    (b)
    there is no moisture in the atmosphere
    (c)
    disturbance moves
    (d)
    both particles as well as disturbance travel from one place to another.

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    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (c)
    (c) The disturbance moves.Air particles only oscillate about a fixed mean position; the moving compression-rarefaction pattern, not the particles, carries the sound energy forward.

  5. Exercise 5

    When we change feeble sound to loud sound we increase its
    (a)
    frequency
    (b)
    amplitude
    (c)
    velocity
    (d)
    wavelength

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (b)
    (b) Amplitude. Loudness tracks amplitude, not frequency, which instead sets the pitch: \(\displaystyle A\uparrow \Rightarrow \text{loudness} \uparrow\).

  6. Exercise 6

    In the curve (Fig.12.1) half the wavelength is
    (a)
    A B
    (b)
    B D
    (c)
    D E
    (d)
    A E
    NCERT_Question_Class9_Science_Exemplar_Ch12_Q6

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (b)
    (b) BD B sits below the crest, D below the adjacent trough — a crest and its next trough are always \(\displaystyle \lambda/2\) apart. AB and DE are only \(\displaystyle \lambda/4\); AE is one full \(\displaystyle \lambda\). Answer: (b) BD

  7. Exercise 7

    Earthquake produces which kind of sound before the main shock wave
    begins
    (a)
    ultrasound
    (b)
    infrasound
    (c)
    audible sound
    (d)
    none of the above

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    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (b)
    (b) Infrasound. An earthquake produces infrasound, frequency \(\displaystyle <20\ \text{Hz}\), before its main shock wave begins, letting sensitive animals sense it and react early.Answer: (b) infrasound.

  8. Exercise 8

    Infrasound can be heard by
    (a)
    dog
    (b)
    bat
    (c)
    rhinoceros
    (d)
    human beings

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    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (c)
    (c) Rhinoceros. Large animals such as the rhinoceros produce and pick up infrasound, using it to communicate over long distances beyond the range of human hearing.

  9. Exercise 9

    Before playing the orchestra in a musical concert, a sitarist tries to adjust
    the tension and pluck the string suitably. By doing so, he is adjusting
    (a)
    intensity of sound only
    (b)
    amplitude of sound only
    (c)
    frequency of the sitar string with the frequency of other musical
    instruments
    (d)
    loudness of sound

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    (c)
    (c) Matching the sitar string's frequency to the other instruments'. Tightening the string raises its frequency, \(\displaystyle T\uparrow \Rightarrow f\uparrow\); the sitarist adjusts tension by ear until the pitches agree.