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Physics · 2022 · 3 marks
CBSE 2022 · Region 5 · Set 2 · Q4
How will the interference pattern in Young's double-slit experiment be affected if: (i) The screen is moved away from the plane of the slits. (ii)…
How will the interference pattern in Young's double-slit experiment be affected if:
(i)
The screen is moved away from the plane of the slits.
(ii)
The source slit is moved away from the plane of the slits.
(iii)
The phase difference between the light waves emanating from the two slits $\displaystyle \mathrm{S}_{1}$ and $\displaystyle \mathrm{S}_{2}$ changes from $\displaystyle 0$ to $\displaystyle \pi$ and remains constant. $\displaystyle 2$ $\displaystyle 2$ $\displaystyle 2$ $\displaystyle 2$ $\displaystyle 3$
Marking-scheme solution
Effect on interference pattern
(i) On moving screen away
(ii) On moving source slit away
(iii) Changing phase difference
i) $\displaystyle \beta=\frac{\lambda D}{d}$
As D increases fringe width increases
(ii)
Fringe width remains same but intensity of fringes decreases.
Alternatively
$\displaystyle \mathrm{s}=$ size of source
$\displaystyle \mathrm{S}=$ distance between source and slit for interference to be seen
$$\frac{s}{s}<\frac{\lambda}{D} \text { remains satisfied }
$$Sharpness of fringes increases/interference pattern may disappear.
There will be no distinct pattern.
(iii)
There will be a dark fringe at the centre instead of a bright fringe.
Alternatively
As the phase difference changes from $\displaystyle 0$ to $\displaystyle \pi$ there will be a shift in pattern on the screen till the central maximum turns to dark fringe.
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