Question

In Young's double slit experiment, the fringe width is 12 mm. If the entire arrangement is placed in water of refractive index `4/3`, then the fringe width becomes (in mm) ______.

Options

• 16

• 9

• 48

• 12

Answer 1

In Young's double slit experiment, the fringe width is 12 mm. If the entire arrangement is placed in water of refractive index `4/3`, then the fringe width becomes (in mm) 9.

Explanation:

Frings width, β = 12 mm

 Refractive index of water, μ = `4/3`

The frings width is given by,

β = `("D"lambda)/"d"`               ...(i)

Here, λ is wavelength of light.

D is distance between screen and source.

d is distance between coherent source.

If the entire arrangement is placed in water then fringes width becomes  β' = `("D"lambda"'")/"d"`             ..... (ii)

Dividing equation (ii) by (i), we have

⇒ `(beta"'")/beta=(lambda"'")/lambda`

⇒ `beta"'"=(12xx3)/4`             `(∵ mu=lambda/(lambda"'"))`

⇒ β = 9 mm