JEE Main 2021 — Wave Optics Question with Solution

The answer is Option B : the distance between consecutive fringes will decrease.

Young's double-slit experiment depends on the principle of interference of light waves, and the resulting pattern of light and dark bands (fringes) depends on the wavelength of the light used.

The formula for the distance between fringes (y) in the double slit experiment is :

y = $$\frac{\lambda D}{d}$$

where :

• λ is the wavelength of the light
• D is the distance from the slits to the screen
• d is the distance between the slits

The wavelength of orange light is approximately 600 nm while the wavelength of blue light is around 475 nm. Therefore, if you change the light from orange to blue, the wavelength λ decreases. As λ is directly proportional to y, if λ decreases, y will also decrease. So, the distance between consecutive fringes will decrease.