Questions while studying for optometry boards

**feel_love217** · 11-19-2005, 06:41 PM

hello harry!!

i hv read all ur thoughts regarding working of power in diff medium and i hv given my thought regarding that. sorry its bit late to talk on that but this is a first time i hv know sumthing like this kinda society exists.
i just want to share thoughts and whts ur approach regarding this..

regards
Amit..

**feel_love217** · 11-19-2005, 08:07 PM

hello everyone!!!

just want to share my thought abt working on power of lens in diff medium and
pls correct me if im wrong as i hvent read any book b4 riting this..

1) radius of curvature stays the same when it is in a diffrent medium. well this is not a assumption but it does stays the same.

in order to work out the the power of lens in water we need to know the radius of curvature in air by the formula:--r=(n'-n/F)
a) r=radius of curvature of lens assumed thin but still can be worked for thick lens with centre thickness, in that case we will work out r1 and r2
b)n'=the refractive index on the lens
c)n=the refrective index of surroundings or medium
d)F=the power of the lens

2)if we know the radius of curvature of any given lens than we can simply drop the lens inside the water, the radius of curvature will not change as radius of curvature is solid and even refractive index of lens will not change(unless we are tired and break the lens or water leak inside the lens)

3) when the lens is droped inside the water, the ray of light will not behave in same fashion as it was doing in air, the reason been water will change its path.

4)as the refractive index of air is 1 which is becoz its ability to change the velocity of light and its properties such as slight bending of light.

5)due to the refractive index of air which is 1.333 and is higher than the air it will bend more light thus light entring more denser medium hv diff focal properties

6) as at intial stage when we wer in air and lens was bringing all the light to a point focus by its ability(pls assume the lens is a best form lens) and that distance frm the lens we called a focal lenght and describe it as dioptre(the actual ability of the lens)

7)as lens are designed to bring rays to point focus this is same lens will try to do the same regardless of any medium and now as ray of light will travel in water it will hit the first surface of lens where the light will find the same curvature but as it will leave the lens it will find a diff medium ie water becoz it will bend more and thus the focal lenght will change and hence the power will change automatically becoz now same lens hv diff ability to bring light into a point focus

8)the way we can find this is by same formula but this time F=(n'-n)/r

where n' will be water ie 1.33 and n will be the refractive index of the lens.

that's what i think abt this quiz!!

thanx for taking out time to read this

pls share ur views

Amit jain (F.B.D.O, smc tech);)