only the central fringe will be white, all other will look colourful. - Using B = 10 43) In Young's experiment, yellow light of wavelength 5890 Å is used. The angular width of the fringes is `0.2^(@)`. How much do you need to change the wavelength to increase the angular width by 10% ?

Options

A. Increase of `589Å`
B. Decreases of `589Å`
C. Increase of `6479Å`
D. No change have to be made in wavelength.

Answer

A

Explanation

Increas of `589Å`
Widht of frings `2(d sin theta)=2(1) lambda`
`:. 2 theta=(2lambda)/(d)` [ for small angle `sin theta- theta`]
In this forumula if d is constant than `theta prop lambda`
`:. (theta_(2))/(theta_(1))=(lambda_(2))/(lambda_(1))`
`theta_(2)=theta_(1)+10% theta_(1)`
`=1.1 theta_(1)`
`:.(theta_(2))/(theta_(1))=(lambda_(2))/(lambda_(1))`
`:. (1. theta_(1))/(theta_(1))=(lambda_(2))/(5890Å)`
`:. lambda_(2)=6479Å`
`:.` Increase in wavelength `=lambda_(2)-labda_(1)`
`=6479-5890`
`=589Å`