#### Waves Book Back Questions

11th Standard

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Physics

Time : 00:45:00 Hrs
Total Marks : 30
5 x 1 = 5
1. A transverse wave moves from a medium A to a medium B. In medium A, the velocity of the transverse wave is 500 ms-1 and the wavelength is 5 m. The frequency and the wavelength of the wave in medium B when its velocity is 600 ms-1, respectively are

(a)

120 Hz and 5 m

(b)

100 Hz and 5 m

(c)

120 Hz and 6 m

(d)

100 Hz and 6 m

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. 3 x 2 = 6
7. The average range of frequencies at which human beings can hear sound waves varies from 20 Hz to 20 kHz. Calculate the wavelength of the sound wave in these limits. (Assume the speed of sound to be 340 m s-1.

8. Sketch y = x −a for different values of a.

9. A mobile phone tower transmits a wave signal of frequency 900MHz. Calculate the length of the waves transmitted from the mobile phone tower.

10. 3 x 3 = 9
11. A baby cries on seeing a dog and the cry is detected at a distance of 3.0 m such that the intensity of sound at this distance is 10-2 W m-2. Calculate the intensity of the baby’s cry at a distance 6.0 m.

12. N tuning forks are arranged in order of increasing frequency and any two successive tuning forks give n beats per second when sounded together. If the last fork gives double the frequency of the first (called as octave), Show that the frequency of the first tuning fork is f = (N−1)n.

13. 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.

14. 2 x 5 = 10
15. Consider a string in a guitar whose length is 80 cm and a mass of 0.32 g with tension 80 N is plucked. Compute the first four lowest frequencies produced when it is plucked.

16. Briefly explain the concept of superposition principle.