Thin film interference—find the height of a wedge

[madfelice]

Homework Statement

Two rectangular pieces of plane glass 11.0 cm long are laid upon the other on a table. At one end they are in contact, at the other end they are separated by a piece of paper, which forms a thin wedge of air. The plates are illuminated at normal incidence by 510 nm light. Interference fringes are observed with 14.0 fringes per centimetre. Find the thickness of the piece of paper.

Homework Equations

2t=m*λ

The Attempt at a Solution

ok, so if I take 2t=m*λ
m=14/0.01*0.011(not sure I have the right number here?)=15.4
so t=(m*λ)/2
t = (15.4(510e-9))/2
t = 3.927e-6
do I have it right or have I messed up m=

 

[BvU]

If there are 14 fringes per centimeter, how many fringes are there on 11 cm ?

 

[madfelice]

I think I have figured it out, I should be multiplying by 0.11, not 0.011, right? That gives me the same answer but one decimal place difference.

 

[BvU]

A factor 10 bigger does not constitute 'the same answer'

It's still a very thin sheet of paper, but no longer unlikely.