Question

In Young's double slit experiment, the wavelength of light was changed from $7000\mathring{A}$ to $3500\mathring{A}$ While doubling the separation between the slits, which of the following is not true for this experiment?

• A. The width of fringes changes.
• B. The colour of bright fringes changes.
• C. The separation between successive bright fringes changes.
• D. The separation between successive dark fringes remains unchanged.

Answer 1

Answer: (D)

As $\beta =\frac{\lambda D}{d}$,
Therefore, when $\lambda$ is halved and $d$ is doubled, $\beta$ becomes ${\frac{1}{4}}^{th}$
The separation between successive dark fringes reduces. It does not remain unchanged.