Choose the incorrect statements from the options given below:(A) If a…

The correct answer is Option (2) → (B) and (D) only

In Young's experiment with slit separation \( d \) and screen distance \( D \), the fringe width and the angular width of a fringe are

    \( \displaystyle \beta = \frac{\lambda D}{d} \qquad \theta = \frac{\beta}{D} = \frac{\lambda}{d} \)

The question asks for the incorrect statements, so each statement is judged as true or false.

(A) If a monochromatic source is replaced by a source of white light in Young's experiment, then interference fringes will be coloured — Correct. Each colour forms its own fringes of width \( \propto \lambda \); the central fringe is white, and the fringes on either side are coloured.

(B) If the screen is moved away from the plane of slits, then the angular width of the fringe will not remain the same — Incorrect. The angular width \( \lambda/d \) does not contain \( D \), so it remains the same; only the linear width \( \beta \) grows.

(C) If separation between slits in Young's experiment is halved, the fringe width becomes double — Correct. \( \beta \propto 1/d \), so halving \( d \) doubles \( \beta \).

(D) The fringe width in Young's experiment is \( \lambda d/D \) — Incorrect. The fringe width is \( \lambda D/d \); \( d \) and \( D \) are interchanged in the statement.