NEET-XII-Physics
17: Light Waves
- #24A double slit S1 - S2 is illuminated by a coherent light of wavelength
λ. The slits are separated by a distance d. A plane mirror is placed in front of the double slit at a distance D1 from it and a screen ∑ is placed behind the double slit at a distance D2 from it (figure 17-E2). The screen ∑ receives only the light reflected by the mirror. Find the fringe-width of the interference pattern on the screen.
Figure
Ans : Given:
Separation between the two slits = d
Wavelength of the coherent light =λ
Distance between the slit and mirror is D1.
Distance between the slit and screen is D2.
Therefore,
apparent distance of the screen from the slits,
`` D=2{D}_{1}+{D}_{2}``
`` \,\mathrm{\,Fringe\,}\,\mathrm{\,width\,},\beta =\frac{\lambda D}{d}=\frac{\left(2{D}_{1}+{D}_{2}\right)\lambda }{d}``
`` ``
Hence, the required fringe width is `` \frac{\left(2{D}_{1}+{D}_{2}\right)\lambda }{d}``.
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