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NCERT Class XII Chapter
Wave Optics
Questions With Solutions

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Question : 4
Total: 21
In a Young’s double-slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment.
Solution:  
Here d = 0.28 mm, D = 1.4 m
Distance of fourth bright fringe from center = 1.2 cm = 1.2 × 10–2 m
Linear position of nth bright fringe , yn =
nDλ
d
Linear position of 4th bright fringe , y4 =
4Dλ
d
1.2 × 10−2 =
4(1.4)λ
0.28×10−3
 , λ = 600 nm
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