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fibre optics

hi i have been given the following question but i am unsure about what i should do :frown:
1) calculate the effective speed of light in
a) a fibre optic glass of refractive index n=1.58
b) fibre optic cladding of refractive index n=1.56

could any1 please explain to my step by step how i would go about answering this question?

thanks

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Reply 1
Avatar for panjabiflower
panjabiflower
OP
1
anyone?
Ok do you know any equations you can use involving a refractive index?
Reply 3
Avatar for panjabiflower
panjabiflower
OP
1
is this one n=sini/sinr
Reply 4
Avatar for Skinnylinny
Skinnylinny
Does this sound familiar?
1n2=c1c2_{1}n_{2} = \frac{c_{1}}{c_{2}}
where 1n2_{1}n_{2} is the refractive index from medium 1 (here it should be a vacuum) to medium 2 (the glass) and c1c2\frac{c_{1}}{c_{2}} is the speed of light in medium 1 (the vacuum) divided by the speed of light in medium 2 (the glass)?
Reply 5
Avatar for panjabiflower
panjabiflower
OP
1
so do you know for q1 part a would the answer be 1.58=speed of light in air/ speed of light in optic glass?
1.58=3*10^8/?
?=3*10^8/1.58
Reply 6
Avatar for Skinnylinny
Skinnylinny
That sounds about right...
Reply 7
Avatar for panjabiflower
panjabiflower
OP
1
i get this on calculator 189873417.7 would i round this to 1.89*10^8
Reply 8
Avatar for panjabiflower
panjabiflower
OP
1
i am unsure about question 1 part b
do i do the same as in q 1a or do i need to divide the refractive index by something first?
Reply 9
Avatar for alex-hs
alex-hs
16
panjabiflower
i get this on calculator 189873417.7 would i round this to 1.89*10^8

if you're doing that, at least round it properly to 1.90*10^8 :wink:
alex-hs
if you're doing that, at least round it properly to 1.90*10^8 :wink:


oh yh stupid mistake - have you got any idea about what i do for question 1 part b?
Reply 11
Avatar for alex-hs
alex-hs
16
panjabiflower
oh yh stupid mistake - have you got any idea about what i do for question 1 part b?

the same as you did for part a, but with the other value for the refractive index. Or am I missing something :confused:
In question 1b you do the same thing as in 1a - speed of light in air and in the new glass instead of the old one... Basically just replace 1.58 with 1.56...
Formula to use is: v=cn\displaystyle v = \frac{c}{n}

v - velocity of light in medium
c - velocity of light in vacuum
n - refractive index of medium
so is answer for part b) 1.92*10^8
Yup! :smile:
does any1 know any equations to work out critical angles?
HINT: what's the angle of refraction at the critical angle?
is it 90 degrees
yup - so sin r = ?

EDIT: And then plug into n = sin i/sin r

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