NTA Abhyas JEE Main2020PhysicsWave OpticsPractice
The effect on the interference fringes if the monochromatic source is replaced by a source of white light would be:
Options
- AInterference pattern disappears
- BFringe separation remains fixed
- CFringe closest to the central fringe is red.
- DFringe separation increases
Correct answer
C. Fringe closest to the central fringe is red.
Step-by-step solution
The interference patterns due to different component colours of white light overlap (incoherently). The central bright fringes for different colours are at same position. Therefore, the central fringe is white. For a point P for which: S 2 P - S 1 P = λ b / 2 λ b ≈ 4000 A ∘ represents the wavelength of blue colour, the blue colour will be absent and the fringe will appear red in colour. Slightly farther away where, S 2 Q - S 1 Q = λ b = λ r / 2 Where λ r ≈ 8000 A ∘ represents the wavelength of red colour, the fring