# Double-slit experiment with two different mediums

How the interference pattern will look like in a double-slit experiment done with two different mediums? Air before the slit and glass after the slit.

• Your figure show the diffraction from a single slit while your text talks about a double slit arrangement. Which do you mean? – dmckee --- ex-moderator kitten Jan 23 '17 at 9:35
• @dmckee Double-slit, because I did find simple Double-slit pic. – Hammar Jan 23 '17 at 11:32

## 2 Answers

The medium that the light travels before it reaches the slits does not affect the result, assuming that the slits are narrow. Only the wavelength of the light matters.

The medium after the slits affects the spacing of the fringes, but qualitatively there is no difference with different media.

There would be no difference qualitatively. The pattern is due to path difference after the slit, which would change by a factor of refractive index $n$ and therefore would change the fringe width compared the case of air..

However, if the upper half is filled with water and bottom half is air, the pattern will change. A little analysis will tell the details of that too.

• On the contrary, the fringe spacing changes because the pattern is due to the phase difference. The relationship between distance and phase is governed by the frequency and the speed of the wave. For light the speed in an medium with index of refraction $n$ is $v = c/n$. – dmckee --- ex-moderator kitten Jan 23 '17 at 9:35
• Oops. You're right. Should I edit the answer or delete it? – Kalpak Gupta Jan 23 '17 at 15:19
• Up to you. You can also edit, wait to see if the downvoers return to amend their votes and delete if the do not. – dmckee --- ex-moderator kitten Jan 23 '17 at 15:35
• No problem. I edited it. Totally deserved the downvotes! – Kalpak Gupta Jan 24 '17 at 7:17