Q 12-10-144JEE MainJEE Main 2019 (11 Jan, Shift 2)Medium
In a double-slit experiment, green light ($5303$ Å) falls on a double slit having a separation of $19.44\ \mu$m and a width of $4.05\ \mu$m. The number of bright fringes between the first and the second diffraction minima is
Answer: (B) $5$
Diffraction minima: $a\sin\theta = \lambda, 2\lambda$. Interference maxima: $d\sin\theta = m\lambda$.
Between the minima, $\dfrac{\lambda}{a} < \sin\theta < \dfrac{2\lambda}{a}$, i.e.
$$\frac da < m < \frac{2d}{a} \Rightarrow 4.8 < m < 9.6$$
$m = 5, 6, 7, 8, 9$: five bright fringes.
Solution by Sreeraj P, M.Sc Physics