Index of refraction for converging lens

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Homework Help Overview

The discussion revolves around determining the index of refraction for a thin converging lens, given its radii of curvature and focal length. The problem involves applying the Lens Maker's equation.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the Lens Maker's equation with the provided values but questions the validity of their result. Participants raise the issue of the sign convention for the radii of curvature, specifically the negative value for R2.

Discussion Status

Participants are actively engaging in checking assumptions related to the sign of R2. A revised calculation has been suggested, leading to a new value for the refractive index, although the discussion does not reach a consensus on the correctness of this value.

Contextual Notes

There is an emphasis on the importance of sign conventions in the context of the Lens Maker's equation, which may affect the calculations and interpretations of the refractive index.

vetgirl1990
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Homework Statement


A thin converging lens has radii of curvature of R1=9cm and R2=-11cm. Assume its focal points F1 and F2 are 5cm from the center of the lens. Determine its index of refraction.

Homework Equations


Len's Makers equation: 1/f = (n2 - n1 / n1) (1/R1 - 1/R2)

The Attempt at a Solution


focal length f = 5cm
n1 = air = 1

Plugging in all my known values:
1/5 = (n2 - 1) (1/9 - 1/11)
n2 = 10.9

This value for refractive index doesn't make sense at all... so I'm not sure what I'm doing wrong!
 
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Did you take into account that R2 is negative?
 
  • Like
Likes   Reactions: vetgirl1990
TSny said:
Did you take into account that R2 is negative?
D'oh! What a ridiculous mistake. Yes, with that taken into account the refractive index is 1.99.
 
OK, good.
 

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