The Young's experiment is performed with the lights of blue λ = 4366 A o and green colour ( λ = 5460 A o ) . If the distance of the 4 t h fringe from the centre is x , then

x B l u e x G r e e n = 5460 4360

Derive the expression for the intensity at a point where interference of light occurs. Arrive at the conditions for maximum and zero intensity.

Let the two waves S 1 and S 2 from the two coherent sources interfere at a point P. Let their amplitudes be a and the initial phase difference between them be ϕ . Then the displacements produced by S 1 and S 2 will be given as: y 1 = a cos ω t ....(i) y 2 = a cos ωt + ϕ ....(ii) The intensity produced by each wave, I 0 ∝ a 2 ....(iii) The resultant displacement at point P will be: y = y 1 + y 2 y = a cos ω t + cos ω t + ϕ y = 2 a cos ϕ 2 cos ω t + ϕ 2 ......(iv) From (iii), it is clear that the amplitude of the resultant displacement is 2 a cos ϕ 2 and therefore the intensity at that point will be: I ∝ 4 a 2 cos 2 ϕ 2 On using (iii), we get: I = 4 I 0 cos 2 ϕ 2 .....(v) Where I 0 is the intensity of each of the individual sources. Using (v) , For ϕ = 0 , ± 2 π , ± 4 π . . . . . , the intensity will be maximum and given by: I = 4 I 0 For ϕ = ± π , ± 3 π , ± 5 π . . . . , the intensity will be zero: I = 0

Light travels in a straight line because

diffraction effect is negligible

it is not absorbed by atmosphere

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IMPORTANT

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In a double-slit experiment, the distance between slits is increased ten times whereas their distance from the screen is halved, then the fringe width

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Important Questions on Optics

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 91

In a double slit experiment using light of wavelength

600 n m

, the angular width of fringe on a distant screen is

0.1 °

. The spacing between the two slits is

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 92

The Young's experiment is performed with the lights of blue

(λ = 4366 \overset{o}{A})

and green colour

(λ = 5460 \overset{o}{A})

. If the distance of the

4^{t h}

fringe from the centre is

x

, then

EASY

12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 93

In Young's double slit experiment, if the two slits are illuminated with separate sources, no interference pattern is observed because,

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 94

A double-slit arrangement produces interference fringes that are

0.25 °

apart using wavelength

600 nm

. If the angular separation is increased to

0.3 °

by changing the wavelength of the light used, then the new wavelength must be

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 95

In Young's double slit experiment, the separation between the slits is halved and the distance between the slits and the screen is doubled. The fringe width is

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 96

In a Young's double slit experiment, the fringe width is

β

. If the entire arrangement is now placed inside a liquid of refractive index $μ$ , the fringe width will become,

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 97

A double-slit apparatus is set up and green light is used to form the interference pattern. The green light is then replaced by red light. Which of the following changes may not allow the spacing of the bright bands on the screen to remain unaffected by the change of light colour? (Given that the distance between the slits is $d$ and that between the plane of the slits and the screen is $D$ .)

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 6 - Optics>Exercise>Q 98

For demonstration of interference, we require two sources which emits radiations of -

In a double-slit experiment, the distance between slits is increased ten times whereas their distance from the screen is halved, then the fringe width

Important Questions on Optics

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