Diffraction in Water
Here is a question that appeared on my optics midterm. The prof did
not post the answers and was unavailable for help. It has been driving me
crazy... "An unexpanded beam from a He-Ne laser is incident on a diffraction
grating. The straight through and the first spectral orders are observed on a
screen. Now the entire setup (laser, grating and screen)is immersed in water.
The pattern on the screen will...
Spread out? Crowd together? Disappear? Remain the same?
What will it do???
I am not very sure but i think that the pattern will spread out.
My reasoning is this : In water the wavelengths will be reduced
as the velocity of light is less, and smaller wavelengths disperse
more. This reasoning will hold only for a diffraction grating as
the dispersion mechanism is independent of the surrounding medium.
In case of a prism, the dispersion will be less as the relative change
in refractive index is small, in which case i think the pattern on
the screen will remain the same.
jasjeet s bagla
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Update: June 2012