Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

If the monochromatic source in Young's double slit experiment is replaced by white light, then:

there will be a central dark fringe surrounded by a few coloured fringes.

there will be a central bright white fringe surrounded by a few coloured fringes.

all bright fringes will be of equal width.

interference pattern will disappear.

Central Maximum: At the central point on the screen, the path difference between the light waves arriving from the two slits is zero ( $\Delta x = 0$ ). The condition for constructive interference ( $\Delta x = n\lambda$ ) is satisfied for all wavelengths (colors) when $n=0$ . Therefore, all wavelengths overlap constructively at the center, resulting in a central white fringe.
Coloured Fringes: For positions away from the center, the path difference is non-zero. The position of the $n$ -th bright fringe is given by $y_n = \frac{n \lambda D}{d}$ . Since the wavelength $\lambda$ varies for different colors ( $\lambda_{red} > \lambda_{violet}$ ), the maxima for different colors occur at different positions. The violet fringe (shortest $\lambda$ ) forms closest to the central maximum, followed by other colors, with red appearing furthest. This results in a few coloured fringes surrounding the central white fringe.
Fringe Width: The fringe width is $\beta = \frac{\lambda D}{d}$ . Since $\lambda$ is different for each color, the fringe widths are not equal.

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