# Looking through a glass hemisphere [closed]

I've found the following question on IsaacPhysics.org . I've been working on it for a couple of hours but I cannot figure it out.

A looking glass is used to read an ancient scroll. This lens has a hemispherical shape with radius R and its flat surface is placed on top of the scroll being examined. The lens is made of glass of refractive index n. The reader is a distance h from the scroll along the axis of symmetry.

What is the minimum value of h for which the entire circular area of the scroll directly under the lens is visible to the observer if $R=3.70\ \rm cm$ and $n=1.30$?

## closed as off-topic by ZeroTheHero, user191954, John Rennie, Kyle Kanos, Jon CusterSep 13 '18 at 12:52

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – ZeroTheHero, Community, John Rennie, Kyle Kanos, Jon Custer
If this question can be reworded to fit the rules in the help center, please edit the question.

• I have tried to workout at what angle there would be total internal reflection from a light ray coming from the edge of the scroll. My reasoning was that at a greater angle than that no light would pass and the scroll would thus not be entirely visible. My difficulty is that this would give a maximal height above which the scroll would no longer visible, eventhough the question specifically asks for a minimal value. – user206444 Sep 12 '18 at 17:58
• I've added an image to the question to further elaborate on my comment. – user206444 Sep 12 '18 at 18:12
• Excellent work. You have solved the problem and shown that the question is incorrectly worded. Minimum should be maximum. Websites and textbooks can contain errors. Have more trust in your own abilities. – sammy gerbil Sep 12 '18 at 18:39