Question

"In a Young’s double-slit experiment, the separation between slits is d and the screen is a distance D from the slits. D is much greater than d and λ is the wavelength of the light. The number of bright fringes per unit width on the screen is: "
A. Dd/λ
B. Dλ/d
C. D/dλ
D. λ/Dd
E. d/Dλ"

Answer 1

Answer:

The number of bright fringes per unit width on the screen is, $x=\dfrac{\lambda D}{d}$      

Explanation:

If d is the separation between slits, D is the distance between the slit and the screen and $\lambda$ is the wavelength of the light. Let x is the  number of bright fringes per unit width on the screen is given by :

$x=\dfrac{n\lambda D}{d}$

$\lambda$ is the wavelength

n is the order

If n = 1,

$x=\dfrac{\lambda D}{d}$

So, the the number of bright fringes per unit width on the screen is $\dfrac{\lambda D}{d}$. Hence, the correct option is (B).