COMEDK20269 May 2026Morning ShiftPhysicsWave OpticsActual
In a Young's double slit experiment, the slit separation is 1.5 mm. The setup is illuminated simultaneously by light of wavelengths 6000 Å and 8000 Å. The screen is placed at a distance of 1.5 m from the slits. It is observed that at a certain point P on the screen which is 4.8mm from the central maximum, fringes due to both the wavelengths coincide. Which of the following options are correct?
Options
- ALight of wavelength 6000 Å produces a dark fringe and light of wavelength 8000 Å produces a bright fringe at P
- BLight of wavelength 6000 Å produces a bright fringe and light of wavelength 8000 Å produces a dark fringe at P
- CLight of wavelength 6000 Å and light of wavelength 8000 Å both produce a dark fringe at P
- DLight of wavelength 6000 Å and light of wavelength 8000 Å both produce a bright fringe at P
Correct answer
D. Light of wavelength 6000 Å and light of wavelength 8000 Å both produce a bright fringe at P
Step-by-step solution
The path difference at point P is given by x = y d D . Substituting the given values: x = 4.8 10⁻³ 1.5 10⁻³ 1.5 = 4.8 10⁻⁶ m. For wavelength ₁ = 6000 10⁻¹⁰ m = 6 10⁻⁷ m, the order of the fringe is: n₁ = x ₁ = 4.8 10⁻⁶ 6 10⁻⁷ = 8 Since n₁ is an integer, a bright fringe is formed at P by ₁ . For wavelength ₂ = 8000 10⁻¹⁰ m = 8 10⁻⁷ m, the order of the fringe is: n₂ = x ₂ = 4.8 10⁻⁶ 8 10⁻⁷ = 6 Since n₂ is also an integer, a bright fringe is formed at P by ₂ . Thus, both wavelengths produce a bright fringe at P. Answer