Question

Assertion :Assertion : When a thin transparent sheet is placed in front of both the slits of Young's experiment, the fringe width will remains same. Reason: Reason : In Young's experiment, the fringe width is directly proportional to wavelength of the source used.

• A. If both assertion and reason are true and reason is the correct explanation of assertion.
• B. If both assertion and reason are true and reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both assertion and reason are false.

Answer 1

The correct option is B If both assertion and reason are true and reason is not the correct explanation of assertion.

Fringe width is given by:

$\beta =\lambda D/d$

Fringe width will remain the same as the waves travel in the air only, after passing through the thin transparent sheet. Due to the introduction of a thin sheet, the path difference is given by :

$\Delta x=\frac{D(\mu -1)t}{d}$

where $\mu$ is the refractive index of the film and t is the thickness of the film.