#### Waves Important Questions

11th Standard

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Physics

Answer all the questions

Time : 01:40:00 Hrs
Total Marks : 50

Part A

10 x 1 = 10
1. Which of the following options is correct?.

 A B (1) Quality (A) Intensity (2) Pitch (B) Waveform (3) Loudness (C) Frequency

Options for (1), (2) and (3), respectively are

(a)

(B),(C) and (A)

(b)

(C), (A) and (B)

(c)

(A), (B) and (C)

(d)

(B), (A) and (C)

2. A sound wave whose frequency is 5000 Hz travels in air and then hits the water surface. The ratio of its wavelengths in water and air is

(a)

4.30

(b)

0.23

(c)

5.30

(d)

1.23

3. Consider two uniform wires vibrating simultaneously in their fundamental notes. The tensions, densities, lengths and diameter of the two wires are in the ratio 8 : 1, 1 : 2, x : y and 4 : 1 respectively. If the note of the higher pitch has a frequency of 360 Hz and the number of beats produced per second is 10, then the value of x : y is

(a)

36 : 35

(b)

35 : 36

(c)

1 : 1

(d)

1 : 2

4. Let y=$\frac{1}{1+x^2}$ at t = 0 s be the amplitude of the wave propagating in the positive x-direction. At t = 2 s, the amplitude of the wave propagating becomes

(a)

0.5m s-1

(b)

1.0m s-1

(c)

1.5m s-1

(d)

2.0m s-1

5. An organ pipe A closed at one end is allowed to vibrate in its first harmonic and another pipe B open at both ends is allowed to vibrate in its third harmonic. Both A and B are in resonance with a given tuning fork. The ratio of the length of A and B is

(a)

$\frac{8}{3}$

(b)

$\frac{3}{8}$

(c)

$\frac{1}{6}$

(d)

$\frac{1}{3}$

6. Speed of sound wave in air.

(a)

Independent of temp

(b)

Increase with pressure

(c)

Increase with increase in humidity

(d)

Decreases with increase in humidity

7. During propagation of a plane progressive mechanical wave

(a)

amplitude of all particules is equal

(b)

particles of the medium executeS.H.M.

(c)

wave velocity depends upon the nature of the medium

(d)

all the above

8. A wave travelling along the x-axis described by the equation y (x, t) = 0.005 cos ($\alpha x-\beta t$). of the wavelength and time period of the wave are 0.08 and 2.0s then and in appropriate units are

(a)

$\alpha=12.50 \pi;\ \beta=\frac{\pi}{2.0}$

(b)

$\alpha=25.00\pi;\ \beta=\overline \pi$

(c)

$\alpha=\frac{0.08}{\pi}\pi;\ \beta=\frac{2.0}{\pi}$

(d)

$\alpha=\frac{0.04}{\pi}\pi;\ \beta=\frac{4.0}{\pi}$

9. An observer moves towards a stationary source of sound with a velocity on fifth of the velocity of sound, what is the percentage increase in the apparent frequency?

(a)

Zero

(b)

0.5%

(c)

5%

(d)

20%

10. A particle on the tough of a wave art any instant will come to the mean position after a time (7= time period)

(a)

$\frac{T}{2}$

(b)

$\frac{T}{4}$

(c)

T

(d)

2T

11. Part B

5 x 2 = 10
12. Which of the following has longer wavelength?

13. An increase in pressure of 100 kPa causes a certain volume of water to decrease by 0.005% of its original volume.
(a) Calculate the bulk modulus of water?.
(b) Compute the speed of sound (compressional waves) in water?.

14. Define wavelength.

15. Consider the following function
(a) y = x2 + 2 $\alpha$ t x
(b) y = (x + vt)2
which among the above function can be characterized as a wave ?.

16. What is the effect of pressure on velocity of sound in gas?

17. Part C

5 x 3 = 15
18. Consider a string whose one end is attached to a wall. Then compute the following in both situations given in figure (assume waves crosses the distance in one second)
(a) Wavelength, (b) Frequency and
(c) Velocity

19. If a flute sounds a note with 450Hz, what are the frequencies of the second, third, and fourth harmonics of this pitch?. If the clarinet sounds with a same note as 450Hz, then what are the frequencies of the lowest three harmonics produced ?.

20. Consider two organ pipes of same length in which one organ pipe is closed and another organ pipe is open. If the fundamental frequency of closed pipe is 250 Hz. Calculate the fundamental frequency of the open pipe.

21. Write the characteristics of wave motion.

22. Derive the Equation of a plane progressive wave.

23. Part D

3 x 5 = 15
24. The ratio of the densities of oxygen and nitrogen is 16:14. Calculate the temperature when the speed of sound in nitrogen gas at 17°C is equal to the speed of sound in oxygen gas.

25. Describe Newton’s formula for velocity of sound waves in air and also discuss the Laplace’s correction.

26. For the travelling : harmonic wave y(x, t) = 2.0 cos 2π [St - 0.0060x + 0.27], where x and yare in cm and t in s. Calculate the phase difference between oscillatory motion of two points seperated by a distance of,
(a) 300 em (b) 0.75 m (c)$\lambda\over 4$