CBSE Class 12 Physics Interference of Light Theory and Examples

CBSE Class 12 Physics Interference of Light Theory and Examples. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

1. PRINCIPLE OF SUPERPOSITION
Two, or more Progressive waves can travel simultaneously in a medium without affecting the motion of one another, Therefore, the resultant displacement of each particle of the medium at any instant is equal to the vector sum of the displacements produced by the two waves separately. This principle is called principle of superposition

Meaning of principle of superposition :
The principle of superposition means that if a number of waves are travelling in a medium, then each one travels independently as if the other waves were not present at all; the shape and other characteristics of any wave are not changed.

2. INTERFERENCE OF TWO WAVES
When two waves of same frequency travel in a medium simultaneously in the same direction then, due to their superposition, the resultant intensity at any point of the medium is different from the sum of intensities of the two waves. At some points the intensity of the resulatant wave is very large while at some other points it is very small or zero. This phenomenon is called the interference of waves.

2.1 Mathematical Interpretation of interference of two waves :
Let us consider two simple harmonic progressive waves of the same frequency travelling in the same direction. Let a1 and a2 be the amplitudes of the waves and φ the phase difference between them at any point in the medium. If the displacements due to these waves at that point be y1 and y2 then.
y1 = a1 sin ωt –––– (i)
and y2 = a sin (ωt + φ) –––– (ii)

ω/2π is the frequency of each wave. By the principle of superposition, the resultant displacement at the point is given by

Thus the resultant intensity at any point depends upon the phase difference φ between the two waves at that point.
Comment : if φ phase diff is equivalent to x path difference or Δt time difference, then remember
φ/2π  =x/ λ=Δt/T

3. TWO TYPES OF INTERFERENCE
(1) Constructive (2) Destructive.
Law of conservation of energy in constructive & Destructive interference :
Energy distributes ununiformly by interference. Neither energy produces nor distroys. It changes from constructive to destructive & from destructive to constructive. Energy redistributes. It follows law of conservation of energy. comparative study of constructive & destructive interference.

Intensity of interference pattern

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