In a two slits experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the slits. If the screen is moved by 5 × 10 - 2 m towards the slits, the change in the fringe width is 3 × 10 - 5 m . If the distance between the slits is 10 - 3 m , calculate the wavelength of light used

The formula used β = λ D d where β is fringe width λ is the wavelength of light D is the distance between slit and screen. d is the distance between slits. Change in fringe width when screen distance from slits is changed by ∆ D is given by ⇒ ∆ β = λ ( ∆ D ) d ⇒ λ = d ( ∆ β ) ∆ D = ( 10 - 3 ) ( 3 × 10 - 5 ) 5 × 10 - 2 ⇒ λ = 6000 A o

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

E M B I B E

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 6

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What are wavefront and its various types ?

Important Questions on Wave Optics

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12th Andhra Pradesh Board

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 7

Explain the reflection of a plane wavefront from a convex mirror.

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12th Andhra Pradesh Board

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 8

Draw a diagram to show the reflection of a plane wavefront which is incident parallel to the principal axis.

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 9

What is Huygen's principle? Explain the optical phenomenon of refraction using Huygen's principle.

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 10

What is total internal reflection. Explain the phenomenon using Huygen's principle.

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12th Andhra Pradesh Board

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 11

A beam of light consisting of two wavelengths, $650 nm$ and $520 nm$ , is used to obtain interference fringes in a Young’s double-slit experiment. Find the distance of the third bright fringe on the screen from the central maximum for wavelength $650 nm$ .

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 12

A beam of light consisting of two wavelengths, $650 nm$ and $520 nm$ , is used to obtain interference fringes in a Young’s double-slit experiment. What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide?

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 13

Define interference of waves.

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 3 - Wave Optics>Exercise>Q 14

In a two slits experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the slits. If the screen is moved by