Question

In a two slit experiment with monochromatic light fringes are obtained on a screen placed at some distance from the sits. If the screen is moved by `5xx10^-2m` towards the slits the change in fringe width is `3xx10^-5m`. If separation between the slits is `10^-3m`, the wavelength of light used
A. (a) `6000Å`
B. (b) `5000Å`
C. (c) `3000Å`
D. (d) `4500Å`

Answer 1

Correct Answer - A
`beta=(lambdaD)/(d)impliesbetapropD`
`impliesbeta_1/beta_2=D_1/D_2implies(beta_1-beta_2)/(beta_2)=(D_1-D_2)/(D_2)implies(Deltabeta)/(DeltaD)=beta_2/D_2=lambda_2/d_2`
`=lambda_2=(3xx10^-5)/(5xx10^(-20))xx10^-3=6xx10^-7m=6000Å`