# Thin Lenses

1. May 4, 2009

### lha08

1. The problem statement, all variables and given/known data
When 2 glass plates form an air wedge with a fine wire at one end, why don't we convert the given wavelength in air of light into the wavelength in glass since we have to convert it when it is entering in water??
Thanks

2. Relevant equations

3. The attempt at a solution

2. May 4, 2009

### mgb_phys

Because the fringes are formed in the air gap - the experiment works just as well with two metal mirrors.

3. May 4, 2009

### lha08

so there are gaps in the glass that light passes through so we don't need to convert it?

4. May 4, 2009

### mgb_phys

The experiment is to measure fringes formed in the air between the two slides.
The only reason you use glass slides is to be able to see what's happening - all the interference takes place in the air (the wedge gap) between them.

5. May 4, 2009

### lha08

If water was surrounding the wedge, would we still keep using the wavelength in air for a problem like that?

6. May 4, 2009

### mgb_phys

If the wedge between the slides is still air, then use air.
If there is water in the wedge between the slides, use water.

7. May 5, 2009

### davieddy

The path difference between the light reflected at either side of the
air wedge is twice the rhickness of the air wedge.

Since only one of the interfering waves passes through the air, I would
say the interference (superposition) occurs anywhere but he air wedge!

Last edited: May 5, 2009