COMEDK Exam 2019 Solved Paper

Given, separation between two slits,
d=0.9‌mm=0.9×10−3m
Distance between slits and screen, D=1m
The distance between two consecutive dark or bright fringes is given as β (fringe width) and that between central fringe and first dark fringe on either side is ‌

β

2

.
It is given that the spacing between second dark fringe and central fringe =β+‌

β

2

=‌

3β

2

As we know, β=‌

λD

d

Hence, ‌

3

2

×‌

λD

d

=1×10−3m
‌⇒‌

3

2

×λ×‌

1

0.9×10−3

=1×10−3m
‌⇒λ=‌

2

3

×10−3×‌

0.9×10−3

1

=0.6×10−6m
∴ Wavelength of monochromatic source of light,
λ=600×10−9m=600‌nm