Answer: Refraction through the two halves of the prism.
- A Refraction through the two halves of the prism
- B Reflection from two separate plane mirrors, as in Fresnel's mirror setup
- C Diffraction of light passing through two narrow physical slits
- D Total internal reflection occurring inside the glass of the biprism
Correct answer: A. Refraction through the two halves of the prism
Explanation: A Fresnel biprism refracts light through its two halves, creating two virtual coherent sources. It is equivalent to YDSE but uses a single physical source split by refraction.
Two coherent slits S₁ and S₂ act as secondary sources; at each point on the screen, the path difference between light from S₁ and S₂ determines whether the waves arrive in phase (bright fringe) or out of phase (dark fringe), producing the characteristic alternating fringe pattern.
Concept context
Huygens principle, Young's double slit, diffraction, polarization. Essential for JEE.