MCQ
This question has a paragraph followed by two statements, Statement $- 1$ and Statement $- 2$. Of the given four alternatives after the statements, choose the one that describes the statements.
A thin air film is formed by putting the convex surface of a plane-convex lens over a plane glass plate. With monochromatic light, this film gives an interference pattern due to light reflected from the top ( convex) surface and the bottom (glass plate) surface of the film.
Statement $- 1$ : When light reflects from the air-glass plate interface, the reflected wave suffers a phase change of $\pi$.
Statement $- 2$ : The centre of the interference pattern is dark.
  • A
    Statement$- 1$ is true, Statement$-2$ is true, Statement$- 2$ is the correct explanation of Statement $- 1.$
  • Statement$- 1$ is true, Statement$-2$ is true, Statement$- 2$ is not the correct explanation of Statement $- 1.$
  • C
    Statement $- 1$ is false, Statement $-2$ is true.
  • D
    Statement$- 1$ is true, Statement$-2$ is false

Answer

Correct option: B.
Statement$- 1$ is true, Statement$-2$ is true, Statement$- 2$ is not the correct explanation of Statement $- 1.$
b
A phase change of $\pi $ rad appears when the ray reflects at the glass - air interface. Also, the centre of the interference pattern is dark.

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