- #1
Clara Chung
- 304
- 14
Homework Statement
A thin flake of mica (n=1.58) is used to cover one slit of a double-slit arrangement.The central point on the screen is occupied by the 7th brigth fringe.If lamda = 550nm, what is the thickness of the mica?
Homework Equations
path difference d=(n-1)*thickness
d=7*lamda
snell's law?
The Attempt at a Solution
first, the paths above the glass must be the same.So they are not in consideration.
let l be the thickness of the glass,t be the length traveled by light in mica,x in air
The mica:
sinθ=nsin∅
sin∅=sinθ/n...(1)
sin∅=l/t..(2)
(1)/(2),
sinθ=nl/t...(3)
In the air:
sinθ=l/x...(4)
compare 4 and 3,
i came out, t=xn.
Then i started to consider the difference of wavelength,
because the wavelength in mica is shorter than in air.
I tried to subtract the sum of the pulses in air and mica and set it equals to 7 lamda,
but what came out is peculiar,
let m , n be the number of pulses in mica and air respectively,f=frequency
m=tf/v...(5)
n=xf/c..(6)
so...
m/n=nt/x
i suppose it being m/n = t/nx ...so that they can be canceled out...
Please help for this:((