1.

In a two slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the slits.If screen is moved by 5 xx 10^(-2) m towards the slits, then change in fringe width is 3 xx 10^(-5) m. If the distance between the slits is 10^(-3) m, calculate the wave length of light used.

Answer»

`6000 Å`
`9000 Å`
`4000 Å`
`5000 Å`

Solution :USING the relation for fringe width, `beta = (lambda D)/(d)`
First CASE : `beta = (lambdaD)/(10^(-3))` ...(i)
Second case : `beta -( 3 xx 10^(-5)) = (lambda(D - 5 xx 10^(-2))/(10^(-3))` ...(ii)
Subtracting (ii) from (i) ` 3 xx 10^(-5) = lambda ( 5 xx 10^(-2))/(10^(-3))`
i.e. `3 xx 10^(-5) = 50 lambda`
WAVELENGTH ` lambda = 3 xx 10^(-5) /50`
`6 xx 10^(-7) m`
`6000 Å`.


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