Read the information given below to answer
In Young’s double slit experiment as shown in figure, interference of light waves were observed on the screen. Thomas Young made two pinholes \( S_1 \) and \( S_2 \) (very close to each other) on an opaque screen in front of parent source \( S \)
\( S_1 \) and \( S_2 \) behaved as coherent sources, and produced interference pattern on the screen which has alternate bright fringe and dark fringes. This experiment proved Huygens’ wave theory of Light.
In YDSE the distance between two consecutive bright fringes is given by 3 mm. What would be the fringe width if YDSE is performed in a medium of refractive index 1.2?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2.5 mm
The distance between two consecutive bright fringes is the fringe width \( \beta = \lambda D/d \). In a medium of refractive index \( \mu \) the wavelength becomes \( \lambda/\mu \), while \( D \) and \( d \) stay the same.
\( \displaystyle \beta' = \frac{(\lambda/\mu)\,D}{d} = \frac{\beta}{\mu} \)
\( \displaystyle \beta' = \frac{3\,\mathrm{mm}}{1.2} = 2.5\,\mathrm{mm} \)