NCERT Exemplar - Physical World Class 11 Notes | EduRev

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Class 11 : NCERT Exemplar - Physical World Class 11 Notes | EduRev

The document NCERT Exemplar - Physical World Class 11 Notes | EduRev is a part of Class 11 category.
All you need of Class 11 at this link: Class 11

Multiple Choice Questions 

Q.1. Water waves produced by a motor boat sailing in water are
(a) Neither longitudinal nor transverse.
(b) Both longitudinal and transverse.
(c) Only longitudinal.
(d) Only transverse.
Ans
. (b)
Solution.
Water waves produced by a motorboat sailing on the surface of deep water are both longitudinal and transverse because the waves, produce transverse as well as lateral vibrations in the particles of the medium. The water molecules at the surface move up and down; and back and forth simultaneously describing nearly circular paths as shown in Figure.

NCERT Exemplar - Physical World Class 11 Notes | EduRev

As the wave passes, water molecules at the crests move in the direction of the wave while those at the troughs move in the opposite direction.

Q.2. Sound waves of wavelength λ travelling in a medium with a speed of v m/s enter into another medium where its speed is 2v m/s. Wavelength of sound waves in the second medium is
(a) λ
(b) λ/2
(c) 2λ
(d) λ
Ans. 
(c)
Solution.
Frequency remains unchanged in both the medium.
So, NCERT Exemplar - Physical World Class 11 Notes | EduRev
λ1 and λ2 are wavelengths and v1 and v2 are speeds in first and second medium respectively.
So, NCERT Exemplar - Physical World Class 11 Notes | EduRev
Hence the wavelength of sound waves in the second medium is 2λ.

Q.3. Speed of sound wave in air
(a) Is independent of temperature.
(b) Increases with pressure.
(c) Increases with increase in humidity.
(d) Decreases with increase in humidity.
Ans.
(c)
Solution. 
We know that speed of sound in air is given by
NCERT Exemplar - Physical World Class 11 Notes | EduRev for air γ ans P are constants.
NCERT Exemplar - Physical World Class 11 Notes | EduRev where ρ is the density of air.
NCERT Exemplar - Physical World Class 11 Notes | EduRev
where ρ1 is density of dry air and ρis density of moist air. Dur to the presence of moisture, density of air decreases.
As NCERT Exemplar - Physical World Class 11 Notes | EduRev
Hence, speed of sound wave in air increases with increase in humidity.

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