Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Diffraction in Water
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A

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

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory