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# In Young'S Double Slit Experiment, Find Out the Intensity of Light at a Point Where Path Difference is λ/3 - Physics

ConceptInterference of Light Waves and Young’S Experiment

#### Questions

In Young's double slit experiment, using monochromatic light of wavelength λ, the intensity of light at a point on the screen where path difference is λ, is K units. Find out the intensity of light at a point where path difference is λ/3.

In Young’s double-slit experiment using monochromatic light of wavelength λ, the intensity of light at a point on the screen where path difference is λ, is units. What is the intensity of light at a point where path difference is λ /3?

#### Solution 1

Phase difference = (2pi)/lambda × Path difference

ϕ1 =(2pi)/lambda × λ = 2π

where ϕ1 is the phase difference when the path difference is λ and the corresonding frequency is I1=K

phi_2=(2pi)/lambdaxxlambda/3=(2pi)/3

where ϕ2 is the phase difference when the path difference is the lambda/3 and the corresponding frequency is I2
Using equation (iv), we get:

I_1/I_2=(4a^2cos^2(phi_1/2))/(4a^2cos^2(phi_2/2))=(cos^2((2pi)/2))/cos^2(((2pi)/3)/2)=(cos^2(ph))/cos^2(pi/3)=1/(1/(2^2))=4

K/I_2=4

I_2=K/4

#### Solution 2

Let I1 and I2 be the intensity of the two light waves. Their resultant intensities can be obtained as:

I' = I_1 + I_2 + 2sqrt(I_1I_2) cos phi

Where,

phi = Phase difference between the two waves

For monochromatic light waves,

I_1 = I_2

:. I' = I_1 + I_1 + 2sqrt(I_1I_1) cos phi

= 2I_1 + 2I_1 cos phi

Phase difference = (2pi)/lambda xx "Path diffrence"

Since path difference = λ,

Phase difference, phi = 2pi

:. I' = 2I_1  + 2I_1 = 4I_1

Given

I’ = K

:. I_1 = K/4    ....(1)

When path difference= pi/3

Phase difference, phi = (2pi)/3

Hence, resultant intensity,  i'_R = I_1 + I_1 + 2sqrt(I_1I_1) cos  (2pi)/3

= 2I_1 + 2I_1(-1/2) = I_1

Using equation (1), we can write:

I_R = I_1 = K/4

Hence, the intensity of light at a point where the path difference is pi/3  is K/4` units

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Solution In Young'S Double Slit Experiment, Find Out the Intensity of Light at a Point Where Path Difference is λ/3 Concept: Interference of Light Waves and Young’S Experiment.
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