(adsbygoogle = window.adsbygoogle || []).push({}); Need to clear confusion on a simple lense problem (solution is worked out :D)

1. The problem statement, all variables and given/known data

The following thin lenses are made of glass

of index of refraction 1.7 and are in air with

index of refraction 1.

Find the focal length of a lens with r1 =

22 cm and r2 = 8 cm.

2. Relevant equations

1/f = (n-1)[(1/R_{1})-(1/R_{2})]

3. The attempt at a solution

n of glass = 1.7

n of air = 1

R_{1}=22 cm

R_{2}= 8 cm

So, I plug it in the above equation

1/f = (1.7 - 1) (1/22 - 1/8)

f = -17.95918367 cm

I need to clear up few concepts.

1)Is f negative because this lens in Diverging (is it diverging? I was expecting the question to mention it! :D)

2)is my working correct? My answer should be negative? Its kind of wierd! :)

3)How do I figure out from the question as to which side is convex and which side is concave?

Thanks! :)

Arshad

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# Homework Help: Need to clear confusion on a simple lense problem (solution is worked out )

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