Define coherent sources of light.

Coherent source of light are those sources which emit continually a light wave having the same frequency, wavelength and in the same phase, or they have a constant phase difference.Coherent sources can be obtained, if the amplitude of an incoming beam of light is divided, This can be done by the process of partial reflection or refraction. These can also be obtained by division of wave front by putting two narrow slits in front of a monochromatic source.

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

Two point sources S 1 and S 2 separated by a distance 10 μ m emit light waves of wavelength 4 μ m in phase. A circular wire of radius 40 μ m is placed around the sources as shown in figure, then ( O is the centre of the circle and O S 1 = O S 2 )

Points A and C are dark and points B and D are bright

Points A and B are dark and points C and D are bright

Points A and B are bright and point C and D are dark

Points A and C are bright and points B and D are dark

E M B I B E

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Interference of Light>Exercise>Q 29

EASY

12th ICSE

IMPORTANT

Earn 100

Which is the most important condition for interference of two waves?

Important Questions on Interference of Light

MEDIUM

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Interference of Light>Exercise>Q 30

State one condition for observing a sustained interference of light.

HARD

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Interference of Light>Exercise>Q 31

What is interference of light? Name the interference happen at a place where intensity of light is maximum and minimum. Write four conditions to sustain interference.

MEDIUM

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Interference of Light>Exercise>Q 32

Thin interference film happens with