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In Young's double slit experiment, a student observes 8 fringes in a certain segment of the screen when a monochromatic light of \mathrm{600nm} wavelength is used. If the wavelength of light is changed to \mathrm{400nm}, then the number of fringes he would observe in the same region of the screen is :

Option: 1

8


Option: 2

9


Option: 3

12


Option: 4

6


Answers (1)

best_answer

Let the length of segment be y

Since there are 8 fringes in that segment

\mathrm{\therefore \quad 8 \beta_{1}=y} \\  ....(1)

\mathrm{\beta_{1}=\frac{\lambda_{1} D}{d}=}  fringe width for wavelength  \mathrm{(\lambda_{1}=600nm)}

Let say there are \mathrm{n_{2}} fringes of wavelength \mathrm{\lambda_{2}=400nm} in segment \mathrm{y}

\mathrm{\therefore n_{2} \beta_{2}=y}      ......(2)

From eqn (1)

\mathrm{8 \beta_{1}=n_{2} \beta_{2}} \\

\mathrm{8 \times \lambda_{1}=n_{2} \lambda_{2}} \\

\mathrm{8 \times 600=n_{2}(400)} \\

\mathrm{n_{2}=12}

hence correct option is 3

Posted by

Rishabh

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