Question

Light from a helium-neon laser (?=633nm) is used to illuminate two narrow slits. The interference pattern is observed on a screen 3.1mbehind the slits. Thirteen bright fringes are seen, spanning a distance of 50mm .

What is the spacing (in mm) between the slits?

Express your answer using two significant figures

Answer 1

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Light from a helium-neon laser (?=633 nm) is used to illuminate two narrow slits. The interference pattern is observed on a screen 3.1 m behind the slits. Thirteen bright fringes are seen, spanning a distance of 51 mm .

What is the spacing (in mm) between the slits?
Express your answer using two significant figures.
d = _____________mm

answer

Given:

wavelength Light from a helium-neon laser

? = 633 x 10 ^-9 m

Distance of th screen from slits D = 3.1 m

Spanning distance y = 51 mm = 51 x 10 ^-3 m

No.of bright finges seen = 13

It si known by the formual for ,

total spaning distance between 13 fringes is :

   y= 12 ?

but ,  ? = ?D / d

So, y = 12 ?D / d

from this spacing between slits:

                         d = 12 ?D / y

                              = 12 ( 633 x 10 ^-9 )(3.1)/51 x 10 ^-3

                              ^{=  461.71 x 10-6    m}