- #1
roam
- 1,271
- 12
Homework Statement
Parallel light in air enters a transparent medium of refractive index 1.33 and is focused 35 mm behind the surface. Calculate the radius of curvature of the surface of the medium
Homework Equations
[itex]f = \frac{R}{2}[/itex]
[itex]\frac{1}{f}=(n-1) \left( \frac{1}{R_1}-\frac{1}{R_2} \right)[/itex]
The Attempt at a Solution
The correct answer must be 8.68 mm, I can't see how they got this answer.
We know that the focus is 35 mm, so if we use the equation
[itex]R=2f=2 \times 35 = 70 \ mm[/itex]
But this is not correct and it doesn't take into account the refractive index.
So, I also tried using the lens-maker's equation:
[itex]\frac{1}{35} = (1.33-1) \left( \frac{1}{R}- 0 \right) \implies R = 17.9[/itex]
I wasn't sure what to use for the second radius so I used 0, and I didn't get the correct answer. So how can I get 8.68 mm?