Chapter No. 8 - Waves

Item-1: 1. 2.

3. 4.

CHAPTER-8 (Waves) Pick True and False: In longitudinal waves particles of the medium vibrate perpendicular to direction of propagation of the wave. A periodic motion is one which repeats itself in equal time intervals. According to Newton’s Formula, velocity of sound in air at 00C is 280 ms-1. Two coherent waves propagating simultaneously along same line will interfere constructively if the path difference between them is (2n +1) λ 2

5. 6. 7.

Item-2:

Two identical waves propagating in opposite direction along the same line give rise to stationary waves. When a transverse wave is reflected from a denser medium, crest is reflected as trough. The wave length of stationary waves set up on a sting is

λ n = 2l

n 8. In a closed organ pipe the wavelength of fundamental note is 4 times the length of the organ pipe. 9. Two turning forks have frequencies 256 Hz and 260 Hz respectively. The number of beats per second are 4. 10. When a listener moves away from a sounding source, the pitch of the sound will decrease. Given below are a few possible answers to each statement of which one is correct, identify the correct one. 1. The wave speed is given by:a).

2. 3.

4.

5. 6. 7.

8. 9.

11.

12.

b).

V=f

λ

c). V=f/λ d). V=T/λ If 20 waves passes through the medium in 1 second with speed of 20 ms-1 then wavelength is:a). 20m b). 2m c). 400m d). 1m The waves in which particles of the medium vibrate parallel to direction of motion are called:a). Transverse waves b). Stationary waves c). Longitudinal waves d). Directional waves The phemenon of passing of waves from one medium into another medium is called:a). Diffraction b). Refraction c). Transmission d). Reflection The distance between two adjacent nodes is:a). λ b). 2λ c). λ / 2 d). λ/4 The number of nodes between two consecutive antinodes is:a). Zero b). 3 c). 2 d). 1 The presence of stationary waves on a string can be easily detected as the motion will be zero at:a). Nodal points b). Antinodal points c). Between node and antinode d). None of these In standing waves if λ = l (length of string) then loops will be:a). 1 b). 2 c). 4 d). 3 The velocity of longitudinal waves in fluid is:a).

10.

V = Tλ

V=√

ρ/E

b).

V=E/ρ

c). V=√E/ρ d). V=ρ/E The discrepancy in the theoretical and experimental values of velocity of sound was corrected by:a). Huygen b). Laplace c). Newton d). Faraday The relation for the velocity of sound in gas is:a). V=γP/ρ b). V=ρP/γ c). V=√γP/ ρ d). The speed of sound is independent of:-

None of these

a). Temperature b). Pressure c). Medium d). source producing sound 13. The velocity of sound is maximum in:a). Air b). Nitrogen c). Metal d). Glass 14. Two waves can interfere only if they have:a). Phase coherence b). Same velocity c). Different frequencies d). Propating in opposite direction 15. The periodic alterations of sound between maximum and minimum loudness are called:a). Constructive Interference b). Diffraction c). Beats d). None of these 16. Beats can be heared when difference of frequency is not more than:a). 8 b). 10 c). 4 d). 6 17. The change in the pitch of sound caused by relative motion of source and listener is called:a). Accoustics b). Laplace’s correction c). Doppler’s effect d). None of these Item-3: Fill in the blanks: 1. Waves transport energy without transporting …………………. 2. The waves which propagate by the oscillation of material particles are called ……….. waves. 3. The waves which do not need a material medium for their propagation are called ………….. waves. 4. An oscillating mass-spring system is an example of …………. Vibrator. 5. In longitudinal wave, particles of the medium vibrate ………… to direction of propagation. 6. The velocity of sound in air increases by ……….. ms-1 per degree rise in temp. 7. For destructive interference, the path difference between interfering waves is ………… 8. Number of beats per second is equal to the ……….. between frequencies of the sources. 9. When a transverse wave is incident on a denser medium from rarer one, it undergoes a phase change of ……… on reflection. 10. The pitch of the sound ……………. When a source moves towards a stationary observer. Item-4:

Match the columns: COLUMN-A 1. The wave which propagate due to oscillation of electric and magnetic field is called. 2. The wave consists of alternately placed 3. The speed of sound in air at t0c is given by 4. The elastic modules E at constant temperature is 5. The speed of sound in hyderogen is 4 times 6. The speed of sound in air at 00C is 7. If two waves of displacement y1, and y2 superimpose then resultant displacement is 8. Two waves of slightly different frequencies and traveling in the same direction 9. When a wave is reflected from a rarer medium crest is reflected as 10. The fundamental frequency of a stationery wave

Item-5: 1. 2. 3. 4. 5. 6. 7. 8.

COLUMN-B Will produce beats 333 ms-1 f1 = 1 / 2 L √ F/m (y1 + y2) Crests and troughs ΔP x V ΔV Vt = V0 + 0.61t Electromagnetic waves Crest Its speed in oxygen

Write short answers: How wavelength and frequency are related with the speed of propagation of a wave? What is the effect of pressure on the speed of sound in a gas? Is it possible for two identical waves traveling in the same direction along a string to give rise to stationary waves? Two waves of slightly different frequencies moving in the same direction along the same line produce beats. How beats are produced? A transverse wave traveling in a denser medium is incident on a rarer medium. How the phase of the wave is affected? How the velocity of a wave will change if “Tension” is made 16 times? How should a sound source move with respect to observer so that frequency of its sound does not change? Why the pitch of sound increases when a listener moves towards a stationery source?

9.

10.

Why Radar can not detect under water objects? Why stars moving towards earth show a blue shift and those moving away show a red shift? ANSWERS

Item-1: 1 2 F T

Pick True and False: 3 4 5 T F T

6 T

7 T

8 T

9 T

10 T

Item-2: 1 b 11 d

M.C.Qs: 3 4 c b 13 14 d a

6 d 16 b

7 a 17 c

8 c

9 b

10 b

2 d 12 c

5 c 15 c

Item-3: Fill in the blanks: 1 2 3 4 Matter Mechanical Electromagnetic Periodic 7 8 9 10 (2n + 1) λ / 2 Difference 1800C Increases Item-4: Match the columns: 1 2 3 E.M Waves Crests and troughs Vt = Vo + 0.61t 6 333ms

-1

5 Parallel

6 0.61

4 ΔP x V ΔV

5 Its speed in oxygen

7

8

9

10

(y1 + y2)

Will produce beats

Crest

f1 = 1 / 2 L √ F/m