# 6 - Interference and differaction Questions Answers

the ratio of intensities between two coherent sound sources is 4:1. the difference of loudness in decibel between maximum and minimum intensities, when they interfere in space is

(1) 10 log2

(2) 20 log3

(3) 10 log3

(4) 20 log2

Asked By: HIMANSHU MITTAL
Joshi sir comment

I1/I= 4/1 so a1/a2 = 2/1 so amax/ amin = 2+1/2-1 = 3/1 so Imax/ Imin= 9/1

now loudness L = 10 log(I/I0)

so difference of loudness = L1-L2 = 10 log (9I/I) = 10 log9 = 20 log3

two coherent light sources A and B with seperation 2λ are placed the x-axis symmetrically about the origin. they emit light of wavelength λ. obtain the position of maximas on a circle of large radius R lying in the xy plane and with the center at origin

Asked By: HIMANSHU MITTAL
Joshi sir comment

for maxima path diffrence should be integral multiple of λ.

It is given that two coherent light sources A and B with seperation 2λ are placed on the x-axis symmetrically about the origin, and we have to get the points of maxima in the circle so at the point where circle cuts the X axis (path diffrence = 2λ) and where circle cuts the Y axis (path difference = 0) will be the point of maxima. Besides it one point will also be present in the circle in first quadrant where path difference will be λ so it will be a maxima also. it means total 8 points are there

two sound waves having intensities 4 unit and 9 unit coming from two coherent sources arrive at a point along the same line simultaneously  in same phase. resultant intensity at the point will be

Asked By: HIMANSHU MITTAL
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Joshi sir comment

Use the formule I = I1 + I2 + 2 √I1 √I2 cosθ

here θ = 0

two sound sources of intensity I and 4I are used in an interference experiment. find the intensity at points where the waves from the two sources are superimposed with a phase difference of

(1) zero

(2) π/2

93)π

Asked By: HIMANSHU MITTAL
Joshi sir comment

Use the formule I = I1 + I2 + 2 √I1 √I2 cosθ

here θ = 0

two waves are represented by y = Acosωt and y = Asin(ωt - π/6), superimpose on each other. the amplitude of the rsultant wave is

Asked By: HIMANSHU MITTAL
Joshi sir comment

first convert cos into sin then calculate phase difference, its value will be π/2 + π/6 = 2π/3

now use the formula for resultant amplitude

which of the following phenomenon cannot be observed with sound waves?

(1) diffraction

(2) polarisation

(3) reflection

(4) interference

Asked By: HIMANSHU MITTAL