Question

In a double-slit experiment, green light (5303 Å) falls on a double slit having a separation of 19.44 µ-m and a width of 4.05 µm. The number of bright fringes between the first and the second diffraction minima is ______.

Options

• 5

• 10

• 9

• 4

Answer 1

In a double-slit experiment, green light (5303 Å) falls on a double slit having a separation of 19.44 µ-m and a width of 4.05 µm. The number of bright fringes between the first and the second diffraction minima is 5.

Explanation:

For diffraction

location of 1^st minime

y₁ = `("D"lambda)/"a"` = 0.2469 Dλ

location of 2^nd minima

y₂ = `(2"D"lambda)/"a"` = 0.4938 Dλ

Now for interference

Path difference at P

`"dy"/"D"` = 4.8λ

path difference at Q

`"dy"/"D"` = 9.6λ

So orders of maxima in between P & Q is 5, 6, 7, 8, 9

So 5 bright fringes all present between P & Q.