JEE MAIN - Physics (2019 - 11th January Evening Slot - No. 26)
In a double-slit experiment, green light (5303$$\mathop A\limits^ \circ $$) falls on a double slit having a separation of 19.44 $$\mu $$m and awidht of 4.05 $$\mu $$m. The number of bright fringes between the first and the second diffraction minima is :
04
05
10
09
Explanation
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For diffraction
location of 1st minima
y1 = $${{D\lambda } \over a}$$ = 0.2469 D$$\lambda $$
location of 2nd minima
y2 = $${{2D\lambda } \over a}$$ = 0.4938 D$$\lambda $$
Now for interference
Path difference at P.
$${{dy} \over D}$$ = 4.8$$\lambda $$
path difference at Q
$${{dy} \over D}$$ = 9.6$$\lambda $$
So orders of maxima in between P & Q is 5, 6, 7, 8, 9
So 5 bright fringes all present between P & Q.
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