Two coherent monochromatic point sources and are placed in front of an infinite screen as shown in figure

Question

Two coherent monochromatic point sources $S_{1}$ and $S_{2}$ are placed in front of an infinite screen as shown in figure. Wavelength of the light emitted by both the sources is $λ$ . Initial phase difference between the sources is zero.

Initially $S_{1} S_{2} = 2.5 λ$ and the number of bright circular rings on the screen in $n_{1}$ . If the distance $S_{1} S_{2}$ is increased and made $5.7 λ$ , the number of bright circular rings becomes $n_{2}$ . The difference $n_{2} - n_{1}$ is:

Smart Achievers · Accepted Answer

(3)

$For S_{1} S_{2} = 2.5 λ, max path difference = 2.5 λ$

$min path difference = 0$

$Between 2.5 λ and 0 lie 2 λ and λ \Rightarrow two circular bright fringes.$

$n_{2} - n_{1}$

$For S_{1} S_{2} = 5.7 λ, max path difference = 5.7 λ$

$min path difference = 0$

$Between 5.7 λ and 0 lie 5 λ, 4 λ, 3 λ, 2 λ, λ \Rightarrow five circular bright fringes.$

$n_{2} = 5$

$∴$ $n_{2} - n_{1} = 5 - 2 = 3$

Solution

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