Question

Two slits 0.1 mm apart are arranged 1.20 m from a screen. Light of wavelength 600 nm from a distant source is incident on the slits.

1. How far apart will adjacent bright interference fringes beon the screen?
2. Find the angular width (in degree) of the first bright fringe.

Answer 1

The distance between adjacent bright fringes (fringe width) in a double-slit interference pattern is given by the formula:

y = `(lambda D)/d`

Where,

y = Distance between adjacent bright fringes

λ = Wavelength of light

D = Distance between the slits and the screen

d = Separation between the slits

1. λ = 600 nm

D = 1.20 m

d = 0.1 mm

y = `(600 xx 10^-9 xx 1.20)/(0.1 xx 10^-3)`

= 7.2 mm

2. The angular width θ of the first bright fringe is given by:

θ = `lambda/d`

= `(600 xx 10^-9)/(0.1 xx 10^-3)`

= 6 × 10⁻³ radian

θ = `6 xx 10^-3 xx 180/pi`

≈ 0.34°