1.

In Young's double slit experiment the separation d between the slits is lambda mm, the wavelength of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20^(@). To increase the fringe angular width to 0.21^(@) (with same lambda. and D) the separation between the slits needs to change to .....

Answer»

`1.7` mm
`1.8` mm
`2.1` mm
`1.9` mm

Solution :In Young.s experiment `d SIN theta_(1)=(B) LAMBDA`
If `theta` is very SMALL, then `sin theta_(1) theta_(1)`
`:. d theta_(1)=lambda`
`:. theta_(1)=(lambda)/(d)`
`:.theta prop (lambda)/(d) [ :. lambda` and n are same]
`:. (theta_(2))/(theta_(1))=(d_(1))/(d_(2))`
`:. (0.21)/(0.20)=(2)/(d_(2)) rArr d_(2)`
`=(2xx0.21)/(0.20)`
`=1.9 mm`


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