WAES( SUB). What is meant by a wave? Ans: The disturbance set up in a medium is known as a wave. What is the property of the medium that is essential for the propagation of mechanical wave? Ans: Elasticity and inertia 3. Which physical quantity does not change when a wave travels from one medium to another? Ans: Frequency. 4. What is a progressive wave? Ans: A wave which travels continuously in a medium in the same direction is called a progressive wave. 5. If y = sin (40t x) represents a progressive wave. What is its frequency? Ans: y = sin (40t x) y = sin 40 (t x/0) comparing this with y = a sin (wt x/v) w = f=40 f=0hz 6. Two waves are represented by the equation y = a sin (wt kx) and Y =a cos (wt kx). What is the phase difference between them? Ans: π radians 7. What is meant by phase of a particle in a wave? Ans: phase of a particle at any instant represents the state of vibration of the particle at that instant. It indicates the relative position of the particle with respect to the origin. 8. What is a mechanical wave? Ans: A wave which requires a medium to propagate is known as mechanical wave 9. Give an example for a two dimensional wave Ans: Light wave. Water waves 0. How does velocity of sound vary with Pressure? Ans: elocity of sound is independent of pressure.. What is a transverse wave? Ans: In a transverse wave, the particles of the medium are vibrating perpendicular to the direction of wave propagation. BYJU s The World s Biggest K- Learning App
0. What is the angle between vibration of particle of medium and direction of propagation of wave in transverse wave? A: 90 0. How does velocity of sound vary with temperature? Ans: elocity of sound is proportional to square root of the temperature. 3. How does velocity of sound vary with humidity? Ans: velocity of sound increases with increase in humidity 5. Why sound travels faster in moist air than in dry air? Ans: Density of moist air is less than that of dry air. As the velocity of sound in gas is inversely proportional to the square root of its density, the velocity of sound in moist air is greater than that of dry air. 6. A wave has a velocity of 330m/s at atmospheric pressure. What will be its velocity at 4 atmospheric pressure? Ans: 330 ms - 7. What are beats? Ans: The rise and fall in the intensity of sound due to super position of two sound waves of slightly different frequencies travelling in the same direction is known as beats 8. What is beat frequency? Ans: The number of beats heard per second is known as beat frequency. 9. Define beat period. Ans: Time interval between two consecutive maxima or minima is called beat period. 0. What is audible range of sound frequencies? Ans: 0 0KHz. By how much do the frequencies of two sound sources differ, if they produce ten beats in two seconds? Ans: Number of beats per second = 0/ = 5f = f f = 5Hz. Define reverberation. Ans: Reverberation is defined as the persistence of audible sound even after the source has ceased to produce the sound. 3. What is stationary wave? Ans: The wave formed due to the super position of two identical waves (having same amplitude and frequency), travelling with same speed, in opposite direction is called a stationary or standing wave. 4. What is fundamental frequency? Ans: The lowest frequency with which a body vibrates is called the fundamental frequency. BYJU s The World s Biggest K- Learning App
5. What are over tones Ans: Frequencies with which a body vibrates which is greater than fundamental frequency is over tones. 6. What are over tones? Ans: Over tones which are integral multiple of the fundamental frequency are called harmonics. 7. The length of vibrating portion of the sonometer wire is doubled. How does the frequency change? Ans: Halved 8. Give the relation between the fundamental note and over tone in open pipe. Ans: f = (n+)f f = fundamental frequency n =,,3 for first and second overtones 9. The fundamental frequency produced in a closed pipe is 500Hz. What is the frequency of the first over tone? Ans: 500Hz 30. Find the distance between node and adjacent antinodes if the wave length is 4m in a stationary wave. Ans: Distance between node and adjacent antinodes are given by; λ 4 = 4 4 = m 3. Explain why is it NOT possible to have interference between the waves produced by sitars? Ans: Because the wave produced will not have a constant phase difference. 3. Which harmonics are present in a closed organ pipe? Ans: All odd harmonic are present in a closed pipe. 33. What will be the resultant amplitude when two waves Y = asinwt and Y =acoswt are superposed at any point at a particular instant? Ans: y = y +y =asinwt + acoswt= a sin wt + π 4 Resultant amplitude= a 34. State the factors in which the speed of a wave travelling along a stretched ideal string depends. Ans: Tension and mass per unit length 35. Fundamental frequency of oscillation of a close pipe is 400Hz. What will be fundamental frequency of oscillation of open pipe of same length? Ans: f e = v/l = 400Hz F o = v/4l f o = f e = X 400 = 800 Hz 36. Why is it difficult some times to recognize your friends voice on phone? Ans: Because of modulation 37. In which of the following media can pass a longitudinal wave pass through? Air, water or iron? Ans: It can pass through all states of matter. BYJU s The World s Biggest K- Learning App
Two Marks Question 38. Explain the different type of waves (based on medium). Ans: waves are classified into two types: i) Mechanical waves: Waves which requires a medium for their propagation are known as mechanical wave. Eg.Waves on the surface of water, seismic waves (due to earth quake), sound waves, waves on a stretched string. ii) Non mechanical wave: waves which do not require a medium for their propagation are known as non mechanicalwae. Eg. Light waves, heat waves radio waves. 39. The equation of a progressive wave is y=0.sin(50t 0.5x). Find the amplitude and magnitude of the velocity,if x and y are in meters. Ans: Given equation is:y = 0.sin(50t 0.5x)= 0.sin 50 (t x/00) Comparing this with y = asin w (t-x/v) Amplitude a= 0.mand elocity v = 00 m/s 40. State the principle of superposition. Name the phenomenon produced due to the superposition of waves. Ans: When two or more waves superpose the resultant displacement of particle of the medium is equal to the vector sum of the displacements due to the individual waves. Superposition of waves leads to the phenomenon of interference, diffraction; beats and formation of stationary waves are due to the superposition at waves. 4. What is a longitudinal wave: Give an example Ans: If the particles of a medium vibrate along the direction of wave propagation then that wave is known as longitudinal wave.eg.sound waves in air are longitudinal waves. 4. The distance between two points is0.m; If the phase difference between these points is / radians. Calculate the wavelength rad Ans: =0.m 0. or 0.4m / 43. How does frequency of a tuning fork change when the prongs are (i)filed (ii)waxed Ans: (i) When the prongs of a tuning fork are filed its frequency increases (ii) The frequency of a tuning fork decreases when the tuning fork is waxed. 44. What is meant by beat? What are its applications? Ans: The periodic rise and fall in the intensity of sound due to its superposition of two sound waves of slightly different frequencies travelling in the same direction are known as beats. BYJU s The World s Biggest K- Learning App
The phenomenon of beat can be used: (i) To determine the unknown frequency of a tuning fork. (ii) In tuning musical instruments. 45. What is Doppler Effect? Given examples Ans: The apparent change in the frequency of sound due to the relative motion between the source and the observer is known as the Doppler effect. Eg. The apparent frequency of the whistle of a train increases as it approaches an observer on the platform and decreases when the train passes the observer. 46. What are the uses of the Doppler effect? Ans: a. Doppler effect is used in radar system to detect the speed of automobiles and aeroplanes. b. It is used in the determination of speed of the submarines c. it is used to determine the speed of stars and planets and other celestial bodies. 47. When two tuning forks A and X are sounded together, they produce 6 beats per seconds. The beat frequency decreases on filing the fork of A. If the frequency of A is 34Hz,what is the frequency of X? Ans: f A = 34Hz f x =?F b = 6beats /s f b =f a fx f x = f A f B = 34 6= 335Hz or 347 Hz. Since the frequency of A increases on filing, and the beat frequency decreases, frequency of X should be more than that of A. Hence its frequency of X =347Hz. 48. What are nodes and antinodes in a stationary wave? Ans: The point in the stationary wave where amplitude of vibration of the particles is zero is called as nodes. The points in a stationary wave where amplitudes of vibration of particles are maximum are called antinodes. 49. An open pipe and closed have the same fundamental frequency. Explain how their lengths are related. Ans: Fundamental frequency of an open pipe = f = / fundamental frequency of a closed pipe = f = /4 Since f = f, l : L = : 50. Mention any four characteristics of a stationary wave. Ans: (i) stationary wave do not move in any direction. (ii) There is no transfer of energy (iii) All the particles in a loop are in the same phase and they are in opposite phase with respect to adjacent loop (iv) Amplitudes are different for different particles. )The fundamental frequency produced in a closed pipe is 00Hz. What are the frequencies of first and second overtone? ANS: first overtone is 300 Hz and second overtone is 500Hz. BYJU s The World s Biggest K- Learning App
t x ) The equation for transverse wave on a string is y = 4 sin with length expressed in centimeter 0.05 50 and time in second. Calculate the wave velocity and maximum particle velocity t x Ans: Given y = 4sin Hence,T = 0.05s, 0.05 50 50cm wave velocity = / T= 50 0 - /5 0 - = 0 ms - dy t x Practical velocity = 4. cos dt 0.05 0.05 50 4 Maximum velocity max = AW = 50. 4 ms - 0.05 3. What is meant by RADAR and SONAR? How are long distancesmeasured using these techniques Ans: RADAR: Radio detecting and ranging SONAR: Sound navigation and ranging The waves produced by the device are sent and are reflected by bodies and reflected them back. If speed of wave is known and time for to and fro journey, the distance can be estimate. Four and Five mark Questions: Ans:. Distinguish between longitudinal and transverse waves. Longitudinal wave Transverse wave. The vibration of particles of the medium is. The vibration of particles of the medium is along the direction of wave propagation perpendicular to the direction of wave propagation. The wave propagates by forming alternate. The wave propagates by forming compressions and rarefactions alternate crests and troughs 3. These waves can travel in solids, liquids 3. These waves can travel in solids and and gases liquid surfaces 4. These waves cannot be polarized 4. These waves can be polarized 5. Distance between two successive 5. Distance between two successive crests or compression or rarefactions is equal to troughs is equal to wave length wave length Ans:. What are the characteristic of progressive wave?. A progressive wave is formed due to continuous vibrations of particles of the medium. The wave travels with certain velocity. BYJU s The World s Biggest K- Learning App
3. Energy and momentum are carried by the wave 4. No particles in the medium are at rest. 5. All particles in medium vibrate with same amplitude 6. Phase changes continuously from particle to particle. 3. State Newton s formula for the velocity of sound in a gas. What is Laplace s correction? Explain Ans: According to Newton. elocity of sound in any medium is given by E v, where E is modulus of elasticity and is density of medium. B For gasses E = B. v =, ---------------------------------------------- () p Newton assumed that propagation of sound in gasses is isothermal, isothermal bulk modulus B =P, pressure of gas. P v, p This is Newton s formula for velocity of sound in a gas. Laplace s correction: Laplace assumed that propagation of sound in gasses is not isothermal, but it s due to adiabatic. Adiabatic bulk modulus for gases B = y P Where y is the ration of specific heats of gas? v = P, This equation is called Newton Laplace s equation. 4) Discuss the variation of velocity of sound with a) Pressure b) Temperature c) Humidity d) wind Ans; a) Effect of pressure According to Boyle s law, at constant temperature pressure of gas of give mass is directly proportional to its density P = constant From the equation P P v, are constant. Thus velocity of sound is independent of pressure b) Effect of temperature BYJU s The World s Biggest K- Learning App
elocity of sound = P P RT ( From ideal gas equation P= m RT m m M M ) v T elocity of sound in gas increases with increase in temperature c) Effect of humidity: presence of water vapour in air reduces the density of air. Density of dry air is greater than moist air. As velocity of sound in moist air is greater than that in dry air. Thus with increase in humidity velocity of sound also increases. d) Effect of wind: Let v, w be the velocity of sound, wind respectively If wind blow in the direction of sound then resultant velocity of sound is (v + w) If wind blows against sound waves then resultant velocity of sound is ( v w) 5) Explain the theory of beats v Ans: Consider two sound waves of same amplitude a and slightly different frequencies n and n traveling in the same direction. The displacement of particle in a time t due to the two waves is. y = a sin w t; y = a sin w t w w t w w t y=a sin cos y = a n n t (n n t sin cos n n t n n t y = A sin wherea a cos is the amplitude of resultant wave. The intensity of resultant of wave is maximum when A is maximum A is maximum when cos n n t = (n n )t i.e 0,,,3 t = 0, 3,,,.. n n n n n n BYJU s The World s Biggest K- Learning App
The interval between successive maxima is T b = n n, The number of times intensity of sound becomes maximum per second is nb =, n n. Hence beat T b frequency is difference between the frequencies of the two waves. 4. Derive general expression for apparent frequency when the source moves toward s the observer and observer moving away from the source. Ans: S S - P ---s------s-----o---- o Consider a source S emitting sound of frequency f. Let v be the velocity of sound. Let the source move towards the observer with a velocity s and the observer move away from source with the velocity 0. In one second source emits f waves such that these waves will be contained in a length S P = s s The apartment wave length of these waves is -------------------------------------() f These waves approach the observer with a relative velocity o The number of waves received by the observer in one second or apparent frequency is s f o o f = f s = o This is the general expression for apartment frequency. 5. Explain how the frequency of tuning force is determined using beats Ans: Consider a tuning fork A of unknown frequency f and other fork B of known frequency f. When A and B are sounded together let m beats are heard per sec. f = f m Let one of the prongs of tuning fork B is loaded with a bit of wax. The two forks are again sounded together let m be used of beats heard per sec BYJU s The World s Biggest K- Learning App
If, i.e. beats increase after adding wax, then the real frequency of B is f = f m If m f m, i.e. beats decrease or remains same after adding wax, then real frequency of B is 6. Distinguish between Stationarywave and Progressive wave. Ans: Stationary wave Progressive wave Stationary wave is formed by superposition of two A progressive wave is formed due to continuous identical progressive waves travelling in opposite vibration of the particles of the medium direction Stationary wave doesn t travel in any direction Progressive wave travels with certain velocity There is no flow of energy Progressive wave transports energy. Particles at the nodes are at rest No particle in medium is at rest Different particles vibrate with different aptitudes All the particles vibrate with same amplitude All the particles in loop are in same phase and they Phase changes continuously from particle to are in opposite phase with respect to particles in particle. adjacent loops 0. What is closed pipe? Show that the overtones in a closed pipe are odd harmonics of the fundamental. (Or) Discuss the modes of vibration of air in a closed pipe. Ans: A pipe opened at one end and closed at other end is called closed pipe f = f m Consider a closed pipe of length L. let be the velocity of sound in air. The air column in a closed pipe vibrates in such a way that always displacement antinodes is formed at opened end and displacement node is formed is closed end. Let f, f, and f 3 be the frequencies and, and 3 be the wave lengths of st, nd and 3 rd modes of vibration respectively. For fundamental mode.: L 4L ;But f f... 4 4L BYJU s The World s Biggest K- Learning App
For nd mode or st overtone: L 3 4L ; But f f... 4 3 4L 3 For 3 rd mode or nd overtone : L 5 4L From (), () and (3) f f : f : 3: 5 : 3 3 ; But f3 f... 3 4 5 3 4L In the case of a closed pipe the frequency of overtones are odd harmonics of the fundamental.. What is an open pipe? Show that overtones in opened pipe are harmonics of fundamental. (Or) Discuss the modes of vibration in an open pipe. Ans: A pipe which is open at both ends is called open pipe. Consider an open pipe of length L. let be the velocity of sound in air. The air column in an open pipe vibrates in such a way that always antinodes are at open ends. Let f, f and f3 be the frequencies and be the wave lengths of st, nd and 3 rd modes of vibration respectively. 5 For fundamental mode: L L ; But f f... L For nd mode or st overtone: L But f f f... L For 3 rd mode or nd overtone : L 3 L 3 3 3 But f3 f3 3f... 3 3 3 L From (), () and (3) f : f ; f 3 = ; : 3 In the case of a closed pipe the frequency of overtones are odd harmonics of the fundamental. BYJU s The World s Biggest K- Learning App
. Derive an expression for fundamental frequency in case of stretched string. Ans: In the fundamental mode of vibration of the string, there will be an antinode in between two nodes at two fixed points. If L is the length of string then L L... elocity of the wave along the string is T... where T is tension in the string and is linear density of the string Fundamental frequency of the string is f, L from eq n () T f, fromeq n () L 3. Derive the equation for a stationary wave. A: The equation of two waves having the same amplitude, wavelength and speed but propagating in opposite directions is, y asin vt xand y asin vt x Where a is the amplitude, is the wavelength and v is the velocity of the wave. The resultant displacement of a particle os given by, y y y asin vt x asin vt x hence we have, y a cos x.sin vt = A sin vt Where A=a cos x represents the amplitude of the resultant wave. 4. Given below are some examples of wave motion. State in each case if the motion is transverse, longitudinal or a combination of both. a) Motion of a kink in a long spring produced by displacing one end of the spring sideways. b) Wave produced in a cylinder containing water by moving its piston back and forth. c) Wave produced by a motor boat sailing in water. BYJU s The World s Biggest K- Learning App
d) Ultrasonic waves in air produced by a vibrating crystal. A: (a) longitudinal wave(b) Transverse wave.(c) Combination of both.(d) Longitudinal wave. 5. What do you mean by wave motion? Discuss its four important characteristics. A: Wave motion is motion where the energy is transferred without the actual movement of the material particles. Four Characteristics: i) It is a simple harmonic motion. ii) Energy is transported without material shift. iii) elocity of waves depends on the medium. (only for the longitudinal waves) iv) The particles oscillate in SHM. 6. A simple harmonic wave is expressed by the equation y = 7 x 0-4 sin( 800t x )Where y and x are in 4.5 centimeter and t is in seconds. Calculate the following. (i) Amplitude. (ii) Frequency. (iii) Wavelength.(iv) Wave velocity(v) Phase difference between two particles separated by 7.0cms. All dimensions are in CGS units. A: y= 7 x 0-4 sin( 800t x ) 4.5 (i) Amplitude = 7 x 0-4 cm. (ii) Frequency f w/ 800 / 400Hz (ii) Wavelength / k 85cm. 4.5 800 (iv) Wave velocity = v = w/k 34000cm s. 4.5 (v0phase difference X Path difference x / 5 rad. 85 7 BYJU s The World s Biggest K- Learning App