How do i demonstrate thin film interference with microscope slides?

[handsomecat]

How do i demonstrate thin film interference with microscope slides?

Textbook questions all mention that you will get parallel fringes when you put a hair between two microscope slides.

However, i have tried doing so, but don't get the parallel fringes. I used a red laser pointer, and a incandescent light bulb.

Is there something that I have missed? Do i need to use polarized light?

 

[Andy Resnick]

I almost always see fringes when two slides or coverslips stick together, no special lighting needed. Try it without the hair?

 

[sophiecentaur]

You get the best results from optically flat and clean slides (dry, too). You also get them, to everyone's annoyance, when you use plane glass holders for 35mm colour slides in an old fashioned slide projector. The colour fringes are often referred to as Newton's rings but they are all sorts of shapes. The smaller the angle, the wider the fringes, of course because they recur each time the spacing increases by a half wavelength. Is your hair 'wispy' or 'coarse'?
You have to get your head in the right place to view the fringes or the direct specular reflection can mask them.

 

[handsomecat]

thanks so much. You are right that the orientation is importont. I saw the fringes!

 

[sardar]

To demonstrate thin film interference with microscope slides, you will need to set up a simple experiment using a light source (such as a laser or incandescent light bulb), two microscope slides, and a thin object such as a hair or a thin piece of plastic. Here is a step-by-step guide on how to conduct this experiment:

1. Set up your light source so that it is shining onto one of the microscope slides at an angle. This will create a thin film of light on the slide.

2. Place the second microscope slide on top of the first one, making sure that it is parallel to the first slide.

3. Place the thin object (hair or plastic) between the two slides, at the edge where the light is shining.

4. Observe the fringes (patterns of light and dark bands) that are created between the two slides.

5. To get a clearer view of the fringes, you can use a polarizing filter on your light source or on the eyepiece of the microscope.

6. If you are using a laser as your light source, make sure it is a monochromatic laser (produces light of only one wavelength) to get a sharper fringe pattern.

7. You may need to adjust the angle of the light source or the slides to get a better view of the fringes.

If you are not getting parallel fringes, there could be a few reasons for this. Make sure that the slides are clean and free of any dust or debris, as this can affect the interference pattern. Also, try using different light sources and objects to see if that makes a difference.

Additionally, it is important to note that the angle of the light source and the thickness of the thin film (created by the two slides and the object) will affect the interference pattern. So, you may need to experiment with these variables to get the desired result.

In summary, to demonstrate thin film interference with microscope slides, you will need to set up an experiment using a light source, two slides, and a thin object, and observe the interference pattern between the slides. It may take some trial and error to get the desired result, but with careful adjustments and attention to detail, you should be able to observe the parallel fringes.