# [Bf-committers] ior

Frédéric van der Essen fred at mentalwarp.com
Sun Apr 3 15:26:42 CEST 2005

```Ooops...
replace "negative" by "<=1" and "positive" by ">=1" in my post and it
should be correct...
Physically, Ior ranges ]0,->[

>indeed it is not negative, if one ior was i_1 than for the opposite
>direction the ior is i_2 = 1/i_1
>
>it comes out from senll's law
>
>
>Anyway
>
>On Sun, 2005-04-03 at 12:56 +0200, Frédéric van der Essen wrote:
>
>
>>Of course it can !
>>the ior isn't lightspeed_in_void / Lightspeed_in_material !!!
>>this is the special case of an object standing in void.
>>
>>the real formula = lightspeed_in_first_material /
>>Lightspeed_in_second_material.
>>
>>if the light goes slower in the first than in the second, then the ior
>>is smaller than one.
>>
>>in the case of a bubble in water, the lightspeed is slower in the water
>>than in the air, so the ior is negative when the light
>>enters the bubble, and positive when the light goes out the bubble.
>>
>>
>>Daniel Barbeau wrote:
>>
>>
>>
>>>ior_of_material  = Lightspeed_in_void /  Lightspeed_in_material
>>>
>>>Lightspeed_in_void is light's maximum speed. 300 000 km/sec If i
>>>recall well.
>>>
>>>Lightspeed_in_material can't be higher than Lightspeed_in_void, so
>>>ior_of_material can't be lower than 1.
>>>
>>>I guess this could be an Elysiun question and an Elysiun answer.
>>>
>>>Dani
>>>
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>>>
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>
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```