CBSE Class 12 Physics 2015 Delhi Set 1 Paper

Question : 21

Total: 26

Answer the following questions:
(a) In a double slit experiment using light of wavelength 600‌nm, the angular width of the fringe formed on a distant screen is 0.1∘. Find the spacing between the two slits.
(b) Light of wavelength 5000Å propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected ?

Solution:

Finding the spacing between two slits Effect on wavelength and frequency of reflected and refracted light
(a) Angular width of fringes
θ=‌

,
where d= separation between two slits
Here θ‌=0.1∘=0.1×‌

180

‌ radian ‌
∴ d‌=‌

600×10−9×180

0.1×π

m
‌=3.43×10−4m
‌=0.34m
(b) For Reflected light: Wavelength remains same Frequency remains same
For Refracted light: Wavelength decreases Frequency remains same

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