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An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency10 GHz. What is the frequency of the microwave measured by the observer?

(a) 17.3 GHz(b) 15.3 GHz(c) 10.1 GHz(d) 12.1 GHzSolutionDoppler effect in light (speed of observer is not very small compared to speed of... View Article

Two stereo speakers are separated by a distance of 2.40 m. A person stands at a distance of 3.20 m directly in front of one of the speakers

Question: Two stereo speakers are separated by a distance of 2.40 m. A person stands at a distance of 3.20 m directly in front of one of the... View Article

A source S and a detector D are placed at a distance d apart. A big cardboard is placed at a distance √2 d from the source and the detector

Question: A source S and a detector D are placed at a distance d apart. A big cardboard is placed at a distance √2 d from the source and the... View Article

A source of sound S and a detector D are placed at some distance from one another. A big cardboard is placed near the detector

Question: A source of sound S and a detector D are placed at some distance from one another. A big cardboard is placed near the detector and... View Article

Two audio speakers are kept some distance apart and are driven by the same amplifier system. A person is sitting at a place 6.0 m from one of the speakers and 64 in from the other. If the sound signal is continuously varied from 500 Hz to 5000 Hz, what are the frequencies for which there is a destructive interference at the place of the listener? Speed of sound in air = 320 m/s.

The path difference of the two sound waves is:ΔL = 6.4 - 6.0 = 0.4 mThe wavelength of either wave = λ = v/f = (320/f) m/sFor destructive... View Article

In Quincke’s experiment, the sound intensity has a minimum value I at a particular position. As the sliding tube is pulled out by a distance of 16.5 mm, the intensity increases to a maximum of 9I. Take the speed of sound in air to be 330 m/s.

(a) Find the frequency of the sound source. (b) Find the ratio of the amplitudes of the two waves arriving at the detector assuming that it does... View Article

In Quincke’s experiment the sound detected is changed from a maximum to a minimum when the sliding tube is moved through a distance of 2.50 cm. Find the frequency of sound if the speed of sound in air is 340 m s^-1.

Distance between maximum and minimum:λ/4 = 2.50 cm=> λ = 2.50 x 4 = 10 cm = 10-1 mAs we know, v = fλor f = v/λ=> f = 340/10-1 = 3400 = 3.4... View Article

The noise level in a classroom in absence of the teacher is 50 dB when 50 students are present. Assuming that on the average each student outputs same sound energy per second, what will be the noise level if the number of students is increased to 100?

β A = 10 log10 (50I/lo) and β B = 10 log10 (100 I/lo)Where, lo is constant reference intensityNow,β B - β A = 10 log10 (100 I/50 I)= 10 log10(2)... View Article

If the sound level in a room is increased from 50 dB to 60 dB, by what factor is the pressure amplitude increased?

Constant reference intensity = Io = 10-12 W/m2The initial intensity is:β1 = 10 log10 (l1/lo)Where, lo is constant reference intensity50 = 10... View Article

Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears?

If sound level = 120 dB then l = intensity = 1 W/m2Audio output = 2W (given)Let x be the closest distance.So, intensity = (2/4πx2) = 1=> x2 =... View Article

If the intensity of sound is doubled, by how many decibels does the sound level increase?

Sound level β1:β1 = 10 log10 (l/lo)Where, lo is constant reference intensityWhen the intensity doubles, the sound level:β2 = 10 log10... View Article

The sound level at a point 5.0 m away from a point source is 40 dB. What will be the level at a point 50 m away from the source?

Sound level = β = 10 log10 (l/lo)As per given statement,βA = 10 log10 (lA/lo)=> lA/lo = 10(β_A/10) ...(1)Again,βB = 10 log10 (lB/lo)=>... View Article

The intensity of sound from a point source is 1.0 × 10^-8 W m^-2 at a distance of 5.0 m from the source. What will be the intensity at a distance of 25 m from the source?

Here l1 = 1 x 10-8 W m-2r1 = 5 m and r2 = 25 ml2 =?We know, l ∝ 1/r2=> l1r12 = l2r22=> l2 = (l1r12)/r22= [1x10-8x25]/[625]= 4 x 10-10 W m-2... View Article

A source of sound operates at 20 kHz, 20 W emitting sound uniformly in all directions. The speed of sound in air is 340 m s^-1 and the density of air is 1.2 kg m^-3.

(a) What is the intensity at a distance of 60 m from the source?(b) What will be the pressure amplitude at this point?(c) What will be the... View Article

Calculate the bulk modulus of air from the following data about a sound wave of wavelength 35 cm travelling in air. The pressure at a point varies between (1.0 × 10⁵ ± 14) pa and the particles of the air vibrate in simple harmonic motion of amplitude 5.5 × 10^-6 m.

Wavelength of sound wave = λ = 35 cm = 35 x 10-2 mPressure amplitude = po = (1 x 105 ± 14) paDisplacement amplitude of the air particles =So =... View Article

Find the change in the volume of 1.0 liter kerosene when it is subjected to an extra pressure of 2.0 × 10⁵ N m^-2 from the following data. Density of kerosene = 800 kg m^-3 and speed of sound in kerosene 1330 m s^-1.

The velocity in terms of the bulk modulus and density :v = √(k/p)where, k = v2 ρ=> k = (1330) 2 x 800 N/m2K = (F/A)/(Δv/Δv)Therefore, ΔV =... View Article

The absolute temperature of air in a region linearly increases from T₁ to T₂ in a space of width d. Find the time taken by a sound wave to go through the region in terms of T₁, T₂, d and the speed u of sound at 273 K. Evaluate this time for T₁ = 280 K, T₂ = 310 K, d = 33m and u = 330 m s^-1.

Temperature variation:T = T1 + [(T2 - T1)x]/dv ∝ √TvT/v = √(T/273)And, dt = dx/vT = du/v (√(273/T))We are given, initial temp = T1 = 280kFinal... View Article

At what temperature will the speed of sound be double of its value at 0°C?

T1 = 273 , v2 = 2v1, v1 = v and T2 = ?We know that, v ∝ √T=> T2/T1 = v22/v12=> T2 = 273 x 22 = 4 x 273 KSo, temp will be (4 x 273) - 273 = 819o C... View Article

The speed of sound as measured by a student in the laboratory on a winter day is 340 m s^-1 when the room temperature is 17°C. What speed will be measured by another student repeating the experiment on a day when the room temperature is 32°C?

velocity of sound = v1 = 340 m/sT1 = 17o C = 17+273 = 290 KLet v2 velocity of sound at temp T2T2 = 32o C = 32 + 273 = 305 KRelation between... View Article

Calculate the speed of sound in oxygen from the following data. The mass of 22.4 litre of oxygen at STP (T = 273 K and p = 1.0 × 10⁵ N m^-2) is 32 g, the molar heat capacity of oxygen at constant volume is Cv = 2.5 R and that at constant pressure is Cp = 3.5 R

p = 1 x 105 N/m2, T = 273 K, M = 32 g and g = 32x10-3 kgv = 22.4 l = 22.4 x10-3 m3Therefore, C/Cv = r = 3.5R/2.5R = 1.4V = √(rp/f) =... View Article