- #1
Arshad_Physic
- 51
- 1
Need to clear confusion on a simple lense problem (solution is worked out :D)
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.
1/f = (n-1)[(1/R1)-(1/R2)]
n of glass = 1.7
n of air = 1
R1 =22 cm
R2 = 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
Homework Statement
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.
Homework Equations
1/f = (n-1)[(1/R1)-(1/R2)]
The Attempt at a Solution
n of glass = 1.7
n of air = 1
R1 =22 cm
R2 = 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