41 + Interview Questions in Waves in Physics – Class 11 Page 1 InterviewSolution

1.	A man jumps from a building with a source of sound. When he reaches halfway down, he starts the siren of frequency 100Hz. A person standing below him on the ground hears the first sound to be of frequency 120Hz. What is the height of the building? Speed of sound = 330m/s. Take g=9.81m/s^2.(a) 154m(b) 308m(c) 77m(d) 500mI got this question by my school principal while I was bunking the class.Asked question is from Waves in portion Waves of Physics – Class 11
Answer» The correct CHOICE is (b) 308m The best EXPLANATION: We can FIND the speed corresponding to the apparent FREQUENCY and then use that to find the height of the building. 120 = 100(330)/(330-v)v = 330 – 3300/12 = 55m/s. Using, v^2 = 2gh, we can find the height covered by the man.The double of this value will be the height of the building as he is mid-way. 55^2 = 29.81hh = 154mHeight of building = 2h = 308m.

Discussion

2.	A man is moving towards a wall with a source of sound in his hand. Frequency of source = 50Hz. Speed of man = 8m/s. If the man sends one pulse of sound, what will be the frequency heard by him after sound reflects off the wall? Speed of sound = 330m/s.(a) 53.86Hz(b) 52.48Hz(c) 51.24Hz(d) 52.45HzI got this question in an international level competition.My doubt is from Waves in division Waves of Physics – Class 11
Answer» The correct OPTION is (B) 52.48Hz For EXPLANATION: First we find frequency heard by wall. That will be 50(330)/(330-8) = 51.24Hz. Now, this will act as source and man will be the listener. So, the frequency heard by the man = 51.24(330+8)/330 = 52.48Hz.

Discussion

3.	If both the source of sound and observer are moving, the apparent frequency will be different from the actual frequency. True or False?(a) True(b) FalseI got this question in unit test.I'm obligated to ask this question of Waves topic in division Waves of Physics – Class 11
Answer» Right OPTION is (b) False Best explanation: If relative MOTION between source and observer is zero there will be no change in frequency heard by the observer. APPARENT frequency only varies in case of relative motion. So the GIVEN STATEMENT is false.

Discussion

4.	A source of frequency 50Hz is moving towards an observer with a deceleration of 2m/s^2. If its initial speed is 20m/s, what will be the maximum frequency heard by the observer? Initial distance between source and observer is 100m. Speed of sound = 330m/s.(a) 47.14Hz(b) 0(c) 53.22Hz(d) 53.03HzI got this question in homework.This intriguing question originated from Waves in portion Waves of Physics – Class 11
Answer» CORRECT option is (c) 53.22Hz Best explanation: Apparent frequency only depends on VELOCITY and not the distance between source and observer.So, MAXIMUM frequency will be HEARD when speed is maximum, which is at the start.F = 50(330)/(330-20) = 53.22Hz.

Discussion

5.	The formula v = √(P/ρ) can be used for any gas considering isothermal process. True or False?(a) True(b) FalseThis question was posed to me in exam.This question is from Speed of a Travelling Wave in chapter Waves of Physics – Class 11
Answer» RIGHT option is (B) False The best I can EXPLAIN: SPEED of longitudinal waves is v = √(B/ρ), where B is bulk modulus. For an isothermal process PV=const. On differentiating, we get: PdV + VdP = 0. ∴ P = -dP/(dV/V) = B. ∴ v = √(B/ρ) = √(P/ρ). We have used the ideal gas equation, so this is only valid for an ideal gas.

Discussion

6.	In case of electromagnetic waves, doppler shifts are independent of whether source moves or observer provided relative speed is the same. True or False?(a) True(b) FalseI have been asked this question in a job interview.My doubt is from Waves in section Waves of Physics – Class 11
Answer» Correct option is (a) True To explain: WHETHER the SOURCE moved or the OBSERVER would only matter if the waves required a material medium to propagate because then the RELATIVE motion between medium and observer would matter.

Discussion

7.	The speed of sound in air is 330m/s. What is the mass of 1 mole of air? Assume it is an ideal gas.(a) 28gm(b) 38gm(c) 20.56gm(d) 29gmI got this question in a job interview.My question is based upon Speed of a Travelling Wave topic in portion Waves of Physics – Class 11
Answer» Right option is (c) 20.56gm Explanation: 1 mole of air occupies 22.4L at STP. Thus, DENSITY ρ = m/22.410^-3. Using EQUATION V = √(P/ρ), we get: v^2 = (P/m)22.410^-3. Pressure at STP = 10^5Pa. ∴ m = (P/v^2)22.410^-3 = 10^5/330^2 22.4*10^-3 = 20.56gm.

Discussion

8.	A source of sound moves towards an observer. What happens to the speed of sound in the medium?(a) Increases(b) Decreases(c) Remains the same(d) Depends on speed with which source movesI have been asked this question in class test.The origin of the question is Waves in section Waves of Physics – Class 11
Answer» Correct option is (c) REMAINS the same To elaborate: SPEED of sound in the medium depends on the properties of the medium like BULK modulus and DENSITY, not on the speed of source creating the sound.

Discussion

9.	A pipe open at both ends has a fundamental frequency of 2Hz. If the pipe is closed at one end and half filled with water, what will be the fundamental frequency?(a) 0.5Hz(b) 2Hz(c) 4Hz(d) 1HzI have been asked this question in class test.Question is from Reflection of Waves topic in chapter Waves of Physics – Class 11
Answer» Right option is (B) 2Hz The BEST explanation: The fundamental frequency in the first case is given by: f1 = v/2L. In the second case length becomes HALF & ONE end is closed, so fundamental frequency F2 = v/(4L/2) = v/2L = f1. So the value of f2 = 2Hz.

Discussion

10.	A pipe is open at both ends. What should be its length such that it resonates a 10Hz source in the 2nd harmonic? Speed of sound in air = 340m/s.(a) 34m(b) 68m(c) 17m(d) 51mThe question was posed to me during an interview.My query is from Reflection of Waves topic in portion Waves of Physics – Class 11
Answer» Right answer is (a) 34m The best I can EXPLAIN: For a PIPE open at both ENDS frequency ‘f’ = nv/2L, where n is speed of sound. Given: f = 10 & n=2. ∴ 10 = 2*340/2L ∴ L = 680/20 = 34m.

Discussion

11.	Two interfering waves have a frequency of 2Hz & 6Hz. What is the beat frequency?(a) 8Hz(b) 4Hz(c) 2Hz(d) 0The question was posed to me in an interview for internship.This interesting question is from Waves topic in chapter Waves of Physics – Class 11
Answer» RIGHT choice is (b) 4Hz Easiest EXPLANATION: Beat FREQUENCY is equal to the difference between FREQUENCIES of interfering waves.In this case, beat frequency = 6-2 = 4Hz.

Discussion

12.	A train with a frequency ‘f’. What will be the frequency heard by a person sitting in the train? Speed of the train is ‘v’.(a) f(b) f(330+v)/330(c) fv/(330-v)(d) fv/(330+v)This question was addressed to me during an interview for a job.My question is taken from Waves in chapter Waves of Physics – Class 11
Answer» Right CHOICE is (a) f To elaborate: There is no RELATIVE motion between the SOURCE and OBSERVER, thus the frequency heard by the person will be the original frequency of the whistle.

Discussion

13.	An observer is standing stationary in air moving at a speed of 2m/s. A source of frequency 20Hz is moving in the direction of wind with speed 10m/s towards the observer. What will be the frequency as heard by the observer? Speed of sound in air is 330m/s.(a) 20.62Hz(b) 19.40Hz(c) 21.68Hz(d) 22.63HzI have been asked this question by my college director while I was bunking the class.The doubt is from Waves topic in section Waves of Physics – Class 11
Answer» CORRECT option is (a) 20.62Hz The best EXPLANATION: As the air is moving, we can solve this QUESTION from the air’s frame of REFERENCE.From the air’s frame of reference, the OBSERVER will be going towards the observer at 2m/sand the source will be coming towards the observer at 10-2 = 8m/s. F = f(v+v0)/(v+v8) = 20(330+2)/(330-8) = 20*332/322 = 20.62Hz.

Discussion

14.	Two longitudinal waves: s1 = 3cos(11t) & s2 = 3cos(10t) interfere. What is the amplitude of the resulting wave?(a) 6cos(0.5t)(b) 6sin(0.5t)(c) 6cos(10.5t)(d) 6sin(10.5t)The question was posed to me in semester exam.I'd like to ask this question from Waves in section Waves of Physics – Class 11
Answer» RIGHT choice is (a) 6COS(0.5t) Easiest EXPLANATION: s = s1+s2 = 2(3)cos(1/2)tcos(21/2)t = 6cos(0.5t)cos(10.5t). The term 6cos(0.5t) corresponds to the AMPLITUDE.

Discussion

15.	If a standing wave is vibrating in the fourth harmonic and the wavelength is λ, what is the length of the string.(a) 2λ(b) λ(c) 4λ(d) λ/4The question was posed to me in an interview for job.My doubt stems from Reflection of Waves in portion Waves of Physics – Class 11
Answer» Correct choice is (a) 2λ For EXPLANATION I would SAY: If the length of string is L, then the wavelength of the standing wave is 2L/N. Or we can say L = nλ/2, where n CORRESPONDS to nth harmonic. ∴ L = 4λ/2 = 2λ.

Discussion

16.	Let’s say we can hear a beat frequency of 2Hz from two tuning forks. The first tuning fork has a frequency of 100Hz. If wax is applied on the 2nd tuning fork, the beat frequency becomes 4Hz, what is the frequency of the 2nd tuning fork?(a) 100Hz(b) 98Hz(c) 106Hz(d) 104HzI have been asked this question in an online interview.My doubt is from Waves in portion Waves of Physics – Class 11
Answer» Right CHOICE is (b) 98Hz Easiest explanation: As the initial beat frequency is 2Hz, the 2nd tuning FORK can have a frequency of 98Hz or 102Hz. When wax is applied to the second tuning fork its frequency should decrease. On doing so the beat frequency has ALSO increased, so the initial VALUE of the frequency of the 2nd tuning fork must be lower than that of the first tuning fork.

Discussion

17.	A wave having an amplitude of 3cm is to be superimposed with another wave of the same amplitude. What should be their phase difference if the net amplitude has to be 0?(a) π/2(b) π(c) 2π(d) 0This question was posed to me in quiz.This intriguing question comes from Principle of Superposition of Waves topic in section Waves of Physics – Class 11
Answer» The correct answer is (B) π Explanation: The net amplitude is GIVEN by: A^2 = A1^2 + A2^2 + 2A1A2cosθ, where θ is the PHASE difference. For A to be ZERO 9 + 9 + 2(9)(9)cosθ = 0 ∴ θ = π.

Discussion

18.	Standing waves can be produced when two identical waves, having a phase difference of π, are travelling in the same direction. True or False?(a) True(b) FalseI have been asked this question in quiz.This interesting question is from Reflection of Waves in section Waves of Physics – Class 11
Answer» Correct answer is (b) False Explanation: The equation of standing waves is given by; y = Asin(kx)COS(WT). This is FORMED by adding two waves of the form asin(kx-wt) & bsin(kx+wt) which shows that they both must be travelling in opposite directions.

Discussion

19.	The equation of a wave is: y = 2sin(4x-3t). What will be the equation of the reflected wave from a free surface?(a) y = 2sin(4x+3t)(b) y = 2sin(3t-4x)(c) y = 2cos(4x+3t)(d) y = 2sin(4x-3t)This question was addressed to me during an online exam.This intriguing question comes from Reflection of Waves in division Waves of Physics – Class 11
Answer» Correct CHOICE is (a) y = 2sin(4x+3t) Explanation: At the FREE SURFACE reflected wave suffers no PHASE change. Only the direction of wave propagation gets reversed. So, the EQUATION will be y = 2sin(4x+3t).

Discussion

20.	In superposition of waves the displacements get added like vectors. True or False?(a) True(b) FalseThe question was posed to me in an interview for job.Question is from Principle of Superposition of Waves in division Waves of Physics – Class 11
Answer» Right answer is (a) True To explain I would SAY: When waves interfere, the RESULTANT DISPLACEMENT is given by vector ADDITION of their individual displacements.

Discussion

21.	What is the minimum distance between a node & an antinode in a standing wave?(a) λ(b) λ/2(c) 2λ(d) λ/4The question was posed to me in an international level competition.This interesting question is from Reflection of Waves topic in division Waves of Physics – Class 11
Answer» Correct answer is (d) λ/4 Explanation: The amplitude in a standing WAVE is given by Asin(kx). Node is a point where amplitude is zero and antinode is a point where amplitude is MAXIMUM. For a node, sin(kx) = 0 kx = 2nπ OR (2π/λ)x = nππ x = nλ/2. For an antinode, sin(kx) = 1 kx = (2n+1)π/2 (2π/λ)x = (2n+1)π/2 x = (2n+1) λ/4. ∴ node is at λ/2, λ, 3λ/2 … & antinode at λ/4, 3λ/4, 5λ/4 … ∴ minimum distance = λ/2 – λ/4 = λ/4.

Discussion

22.	A source moves towards a stationary observer with a speed of 10m/s. If the frequency of the source is 10Hz what will be the wavelength of sound heard by the observer? Speed of sound = 330m/s.(a) 32m(b) 34m(c) 33m(d) 31mThe question was asked during an online interview.My question is taken from Waves topic in section Waves of Physics – Class 11
Answer» CORRECT answer is (a) 32m For EXPLANATION: Apparent frequency F = f(330+v0)/(330+v8) = 10(330)/(330-10) = 10.31Hz. Wavelength = 330/F = 330/10.31 = 32.007m = 32m.

Discussion

23.	If a string wave encounters a completely fixed end, what happens to its phase?(a) Stays the same(b) Changes by π(c) Changes by π/2(d) Waves gets destroyedI got this question in a national level competition.Enquiry is from Reflection of Waves in chapter Waves of Physics – Class 11
Answer» Correct CHOICE is (b) Changes by π To explain I WOULD say: The reason for the PHASE to change by π is that the boundary displacement should be zero because it is rigid & by principle of superposition it is only possible if the reflected wave differs by a phase of π.

Discussion

24.	In a standing wave the amplitude of a particle is fixed, but varies from particle to particle. True or False?(a) True(b) FalseThe question was asked in an online interview.This is a very interesting question from Reflection of Waves topic in section Waves of Physics – Class 11
Answer» The correct choice is (a) True To explain: A standing wave neither MOVES LEFT or right, all particles between two nodes are in the same phase.The equation of a standing wave is of the FORM Asin(kx)COS(wt), where Asin(kx) is the amplitude which is different for different values of X. This shows that for each value of x we get a different value of amplitude.

Discussion

25.	Consider the phenomenon of beats & select the correct statement.(a) It occurs when frequencies are close or equal(b) It correspond to the change in intensity we hear due to interference of 2 waves having close frequencies(c) It corresponds to a constant intensity sound heard during wave interference(d) Beat frequency is variableThis question was posed to me during an interview.My query is from Waves topic in section Waves of Physics – Class 11
Answer» The correct ANSWER is (b) It correspond to the change in intensity we HEAR due to interference of 2 WAVES having close frequencies Best explanation: When two waves with close, but not equal, frequencies interfere, beats are produced. They have a frequency equal to the average frequency of the two interfering waves and we recognize them as the variable intensity SOUND we hear.

Discussion

26.	y1 = 2sin(3x – 2t) & y2 = 3sin(3x – 2t + π/4). Find the expression for resultant displacement caused by superposition of the two waves.(a) 3.6sin(2x-3t+3π/7)(b) 4.63sin(3x-2t+3π/5)(c) 3.6cos(3x-2t+3π/7)(d) 4.63cos(3x-2t+3π/5)I have been asked this question during an interview for a job.I would like to ask this question from Principle of Superposition of Waves in portion Waves of Physics – Class 11
Answer» The correct answer is (b) 4.63sin(3x-2t+3π/5) EXPLANATION: y = y1 + Y2= 2SIN(3x-2t) + 3sin(3x-2t+π/4) = Asin(3x-2t+φ). A^2 = A1^2 + A2^2 + 2A1A2cosθ,where θ = π/4, A1 = 2 & A2 = 3. ∴ A = sqrt(4+9+12/√2) = 4.63m. Tanφ = A2sinθ / (A1 + A2cosθ) = (3/√2)/(2+3/√2) = 0.51.∴ φ = 27rad. ∴ y = 4.63sin(3x-2t+8.6π)= 4.63sin(3x-2t+3π/5).

Discussion

27.	Consider standing waves in an air column with one end closed. What is a pressure node?(a) Pressure variation is maximum(b) Displacement variation is minimum(c) Same as displacement node(d) Least pressure changeThe question was asked by my college director while I was bunking the class.My doubt is from Reflection of Waves topic in chapter Waves of Physics – Class 11
Answer» Right choice is (d) Least pressure change For explanation: The point where there is an antinode corresponds to maximum amplitude of displacement. This ALSO implies that here, pressure changes are MINIMUM and it is THEREFORE called a pressure node.

Discussion

28.	Laplace correction makes use of which of the following processes?(a) Isothermal(b) Adiabatic(c) Isochoric(d) IsobaricThe question was posed to me in an international level competition.My doubt stems from Speed of a Travelling Wave topic in section Waves of Physics – Class 11
Answer» RIGHT choice is (b) ADIABATIC Explanation: Laplace SAID that during propagation of sound energy there isn’t enough TIME for heat to flow and maintain temperature, so he considered the PROCESS to be adiabatic.

Discussion

29.	Consider the case of normal modes of vibration for the air column with only one end closed. What is the length of the air column for the fundamental harmonic?(a) λ/2(b) λ(c) 2λ(d) λ/4I got this question in an online quiz.Asked question is from Reflection of Waves topic in portion Waves of Physics – Class 11
Answer» Right answer is (d) λ/4 The best I can explain: For the GIVEN CONDITION wavelength is RELATED to length by: λ = 4L/(2n+1). ∴ For fundamental harmonic n=0, & L = (2n+1)λ/4 = (0 + 1)λ/4 = λ/4.

Discussion

30.	What is the ratio of speed of sound in air when measured after laplace correction to that measured by Newton’s formula?(a) 1.18(b) 0.84(c) 1.4(d) 0.71The question was asked during an internship interview.I need to ask this question from Speed of a Travelling Wave in portion Waves of Physics – Class 11
Answer» RIGHT answer is (a) 1.18 Explanation: By Newton’s FORMULA v = √(P/ρ) & after LAPLACE’s correction v = √(P/ρ), whereis ratio of specific heats of air. The ratio of speeds = √γ. For air γ = 7/5 & the ratio of speeds = √(7/5) = 1.18.

Discussion

31.	What does the given equation: x = Asin(ky+wt+a) represent?(a) Wave travelling along positive x direction(b) Wave travelling along negative x direction(c) Wave travelling along positive y direction(d) Wave travelling along negative y directionThe question was posed to me during an interview for a job.My question is based upon Displacement Relation in a Progressive Wave in section Waves of Physics – Class 11
Answer» RIGHT answer is (d) Wave travelling along negative y direction The explanation is: A way of looking at a travelling wave is CONSIDERING the direction in which a particular value of TRANSVERSE displacement moves.For the GIVEN equation x = Asin(ky+wt+a) we have to see the direction in which x moves.For eg: If we CONSIDER the amplitude A, for x =A as t increases, y should decrease.So, we can say that the wave propagates in the negative y direction.

Discussion

32.	Why is the speed of longitudinal waves sound in solids greater than that in liquids?(a) Solids have lesser bulk modulus(b) Gases have lesser density(c) Solids have greater bulk modulus and density than gases but increase in bulk modulus dominantes over increase in density(d) Gases don’t have lesser particles in a given volume and therefore transfer sound energy slowlyThis question was posed to me during an interview.My question is based upon Speed of a Travelling Wave topic in section Waves of Physics – Class 11
Answer» CORRECT option is (c) Solids have greater BULK modulus and density than gases but increase in bulk modulus dominantes over increase in density Easy EXPLANATION: Speed is EXPRESSED as √(B/ρ). For solids B and ρ is greater than that of gases but an increase in B compensates over the increase in ρ,and thus speed is greater in solids.

Discussion

33.	A string has a mass of 100gm & is under a tension of 10N. What should be its length if the speed of transverse waves is to be 10m/s on the string.(a) 1.8m(b) 10m(c) 1m(d) 2mThe question was asked in an interview.I would like to ask this question from Speed of a Travelling Wave topic in chapter Waves of Physics – Class 11
Answer» The CORRECT ANSWER is (c) 1M To elaborate: v = √(T/μ), μ = M/L. V^2 = TL/M Or L = v^2M/T = 100 * 0.1/10 = 1m.

Discussion

34.	All waves require material for propagation. True or False?(a) True(b) FalseThis question was addressed to me in an international level competition.This interesting question is from Transverse and Longitudinal Waves in division Waves of Physics – Class 11
Answer» Right option is (B) False Easy EXPLANATION: Only material waves,like the name suggests, require material for PROPAGATION. Electromagnetic waves on the other hand don’t require any medium. They can travel through vacuum in the FORM of ELECTRIC and magnetic fields.

Discussion

35.	A sinusoidal wave has an amplitude of 3cm. Time period is 1s. The wavelength is 1cm. And at x = 0, t=0 the particle is at its mean position & moving upwards. What is the equation of the wave if it is travelling along the positive x-axis?(a) y = 3sin(2πx – 2πt)(b) y = 3sin(2πt – 2πx)(c) x = 3sin(2πt – 2πy)(d) y = 3cos(π + 2πt – 2πx)I got this question in an internship interview.This key question is from Displacement Relation in a Progressive Wave topic in division Waves of Physics – Class 11
Answer» Correct answer is (b) y = 3sin(2πt – 2πx) Explanation: The wave number k = 2π/1 = 2π. The ANGULAR frequency W = 2π/1 = 2π. The particle at x=0, t=0 is moving up from its mean POSITION, & the wave travels towards the positive x-axis so the equation will be: y = 3sin(2πt – 2πx).

Discussion

36.	What is the expression for wave speed in the given equation: y = Asin(kx-wt + π)?(a) dy/dt(b) w/k(c) 2πw/k(d) 2πk/wThe question was posed to me during an online exam.I would like to ask this question from Speed of a Travelling Wave in division Waves of Physics – Class 11
Answer» The correct answer is (b) w/k Best explanation: The distance moved by a PARTICULAR value of displacement per UNIT time is called wave SPEED.Basically, we have to study the motion of a fixed phase along the direction of wave propagation.So, kx – wt = constant.On differentiating we get: KDX – wdt = 0 dx/dt = w/k, which is the wave speed.

Discussion

37.	An equation of a wave is given by: y = 2sin(3x-2t+π/2). What is the minimum distance between two points having the same phase?(a) 3(b) π/2(c) 2π/3(d) πThe question was asked in examination.Origin of the question is Displacement Relation in a Progressive Wave in chapter Waves of Physics – Class 11
Answer» The CORRECT answer is (c) 2π/3 Best explanation: In the GIVEN equation the phase is 3x-2t+π/2. This is repeated after every 2π. ∴ sin( 3x-2t+π/2) +2nπ = sin( 3x-2t+π/2).We can consider the case at t=0, sin(3x+π/2) = sin(3x+π/2+2nπ)OR cos(3x) = cos(3x+2nπ)∴ n = 1 for MINIMUM difference.Minimum distance can be FOUND from KX = 2πOR x = 2π/k = 2π/3.

Discussion

38.	Transverse waves involve energy transfer by movement of medium particles, while longitudinal waves don’t. True or False?(a) True(b) FalseThis question was posed to me in exam.The doubt is from Transverse and Longitudinal Waves topic in section Waves of Physics – Class 11
Answer» The correct choice is (b) False The best explanation: Transverse waves involve vibration, & not MOVEMENT, of MEDIUM particles to TRANSFER energy. Even in LONGITUDINAL waves, medium particles move up & down but don’t travel to transfer energy.

Discussion

39.	Electromagnetic waves are considered to be which of the following types?(a) Transverse(b) Longitudinal(c) Both Transverse & Longitudinal(d) Neither longitudinal nor transverseThis question was addressed to me in class test.My enquiry is from Transverse and Longitudinal Waves in chapter Waves of Physics – Class 11
Answer» Right answer is (a) TRANSVERSE For explanation: Electromagnetic waves are formed by transverse MOTION of electric & magnetic fields. THUS, they are said to be transverse waves.

Discussion

40.	A sinusoidal wave has an amplitude of 2cm. It is travelling in the negative x-direction. The distance between two crests is 2cm. The angular frequency is πs^-1. What is the displacement of the particle at x = 20.5cm, at t = 10s? Assume that at t=0 & x=0 the particle was at the mean position and going downwards. ‘x’ &’y’ are in cm.(a) 0cm(b) 1cm(c) -1cm(d) -2cmThe question was posed to me in quiz.The doubt is from Displacement Relation in a Progressive Wave topic in section Waves of Physics – Class 11
Answer» Right CHOICE is (d) -2CM Easy explanation: The equation suiting the given CONDITIONS will be: y = ASIN(kx+wt+a) At x=0, t=0, velocity is negative, so ‘a’ will be π. k = 2π/λ = π. ∴ y = 2sin(πx + 2T + π). At x=20cm & t=10s, y = 2sin(20.5π + 10π + π) = 2sin(31.5π) = -2cm.

Discussion

41.	The equation of a wave is given by y = 3sin(4x-2t). What is the time period and wavelength of the wave?(a) T = 2π, λ = 2π(b) T = π, λ = 2π(c) T = π, λ = π/2(d) T = π/2, λ = πThe question was asked during an interview.This interesting question is from Displacement Relation in a Progressive Wave in portion Waves of Physics – Class 11
Answer» Correct OPTION is (c) T = π, λ = π/2 The BEST I can explain: From the equation we GET: k=4 & w=2. Wavelength is GIVEN by 2π/k = 2π/4 = π/2. TIME period = 2π/w = 2π/2 = π.

Discussion

Explore topic-wise InterviewSolutions in .

If both the source of sound and observer are moving, the apparent frequency will be different from the actual frequency. True or False?(a) True(b) FalseI got this question in unit test.I'm obligated to ask this question of Waves topic in division Waves of Physics – Class 11

The formula v = √(P/ρ) can be used for any gas considering isothermal process. True or False?(a) True(b) FalseThis question was posed to me in exam.This question is from Speed of a Travelling Wave in chapter Waves of Physics – Class 11

In case of electromagnetic waves, doppler shifts are independent of whether source moves or observer provided relative speed is the same. True or False?(a) True(b) FalseI have been asked this question in a job interview.My doubt is from Waves in section Waves of Physics – Class 11

The speed of sound in air is 330m/s. What is the mass of 1 mole of air? Assume it is an ideal gas.(a) 28gm(b) 38gm(c) 20.56gm(d) 29gmI got this question in a job interview.My question is based upon Speed of a Travelling Wave topic in portion Waves of Physics – Class 11

Two interfering waves have a frequency of 2Hz & 6Hz. What is the beat frequency?(a) 8Hz(b) 4Hz(c) 2Hz(d) 0The question was posed to me in an interview for internship.This interesting question is from Waves topic in chapter Waves of Physics – Class 11

Two longitudinal waves: s1 = 3cos(11t) & s2 = 3cos(10t) interfere. What is the amplitude of the resulting wave?(a) 6cos(0.5t)(b) 6sin(0.5t)(c) 6cos(10.5t)(d) 6sin(10.5t)The question was posed to me in semester exam.I'd like to ask this question from Waves in section Waves of Physics – Class 11

If a standing wave is vibrating in the fourth harmonic and the wavelength is λ, what is the length of the string.(a) 2λ(b) λ(c) 4λ(d) λ/4The question was posed to me in an interview for job.My doubt stems from Reflection of Waves in portion Waves of Physics – Class 11

Standing waves can be produced when two identical waves, having a phase difference of π, are travelling in the same direction. True or False?(a) True(b) FalseI have been asked this question in quiz.This interesting question is from Reflection of Waves in section Waves of Physics – Class 11

In superposition of waves the displacements get added like vectors. True or False?(a) True(b) FalseThe question was posed to me in an interview for job.Question is from Principle of Superposition of Waves in division Waves of Physics – Class 11

What is the minimum distance between a node & an antinode in a standing wave?(a) λ(b) λ/2(c) 2λ(d) λ/4The question was posed to me in an international level competition.This interesting question is from Reflection of Waves topic in division Waves of Physics – Class 11

If a string wave encounters a completely fixed end, what happens to its phase?(a) Stays the same(b) Changes by π(c) Changes by π/2(d) Waves gets destroyedI got this question in a national level competition.Enquiry is from Reflection of Waves in chapter Waves of Physics – Class 11

In a standing wave the amplitude of a particle is fixed, but varies from particle to particle. True or False?(a) True(b) FalseThe question was asked in an online interview.This is a very interesting question from Reflection of Waves topic in section Waves of Physics – Class 11

Laplace correction makes use of which of the following processes?(a) Isothermal(b) Adiabatic(c) Isochoric(d) IsobaricThe question was posed to me in an international level competition.My doubt stems from Speed of a Travelling Wave topic in section Waves of Physics – Class 11

All waves require material for propagation. True or False?(a) True(b) FalseThis question was addressed to me in an international level competition.This interesting question is from Transverse and Longitudinal Waves in division Waves of Physics – Class 11

What is the expression for wave speed in the given equation: y = Asin(kx-wt + π)?(a) dy/dt(b) w/k(c) 2πw/k(d) 2πk/wThe question was posed to me during an online exam.I would like to ask this question from Speed of a Travelling Wave in division Waves of Physics – Class 11

Transverse waves involve energy transfer by movement of medium particles, while longitudinal waves don’t. True or False?(a) True(b) FalseThis question was posed to me in exam.The doubt is from Transverse and Longitudinal Waves topic in section Waves of Physics – Class 11