In: Physics
Light from a helium-neon laser
(? = 633 nm) is used to illuminate two narrow slits.
The interference pattern is observed on a screen 3.3m behind the
slits. Eleven bright fringes are seen, spanning a distance of 54mm
.
What is the spacing (in mm) between the slits?
wavelength Light from a helium-neon laser
? = 633 x 10 -9 m
Distance of th screen from slits D = 3.3 m
Spanning distance y = 54 mm = 54 x 10 -3 m
No.of bright finges seen = 11
It si known by the formual for ,
total spaning distance between 11 fringes is :
y = (11-1) ? = 10?
but , ? = ?D / d
So, y = 10 ?D / d
from this spacing between slits:
d = 10 ?D / y
= 10( 633 x 10 -9 )(3.3)/54 x 10 -3
= 386.83x10-6 m
= 0.387 mm (rounded)